White glass-ceramic substrates and articles including tetragonal zirconia crystalline phase, and method of manufacturing the same

ABSTRACT

A glass-ceramic article comprises: a center-volume composition comprising (on an oxide basis): 55-75 mol % SiO 2 ; 0.2-10 mol % Al 2 O 3 ; 0-5 mol % B 2 O 3 ; 15-30 mol % Li 2 O; 0-2 mol % Na 2 O; 0-2 mol % K 2 O; 0-5 mol % MgO; 0-2 mol % ZnO; 0.2-3.0 mol % P 2 O 5 ; 0.1-10 mol % ZrO 2 ; 0-4 mol % TiO 2 ; and 0-1.0 mol % SnO 2 . Lithium disilicate and either β-spodumene or β-quartz are the two predominant crystalline phases (by weight) of the glass-ceramic article. The glass-ceramic article further comprises tetragonal ZrO 2  as a crystalline phase. The composition of the glass-ceramic article from a primary surface into a thickness of the glass-ceramic article can comprise over 10 mol % Na 2 O (on an oxide basis), with the mole percentage of Na 2 O decreasing from the primary surface towards the center-volume. The glass-ceramic article exhibits a ring-on-ring load-to-failure of at least 120 kgf, when the thickness of the glass-ceramic article is 0.3 mm to 2.0 mm.

RELATED APPLICATIONS

This application claims the benefit of priority to U.S. ProvisionalApplication No. 63/045,934, filed Jun. 30, 2020, the contents of whichare incorporated herein in their entirety.

BACKGROUND

Glass-ceramic materials that appear opaque and white in color have beenutilized as cooktop plates, cooking utensils, and in mobile devices(such as smart phones) among other things. However, there is a problemin that these glass-ceramic materials have less than optimal mechanicalproperties, in particular less than optimal damage resistance andfracture toughness.

SUMMARY

The present disclosure addresses that problem with glass-ceramicsubstrates having a SiO₂—Al₂O₃—Li₂O—P₂O₅—ZrO₂ composition, lithiumdisilicate and either β-spodumene solid solution or β-quartz solidsolution as the two predominant crystalline phases, and tetragonal ZrO₂as an additional crystalline phase. The glass-ceramic substrates areion-exchanged into glass-ceramic articles having particular Na₂Oconcentration as a function of thickness profiles. The glass-ceramicarticles, even when having a thickness of 0.3 mm to 2.0 mm, exhibitexceptional mechanical performance. For example, the glass-ceramicarticles (after being subjected to an ion-exchange procedure) exhibit aring-on-ring load-to-failure of at least 120 kgf, and, after beingabraded with SiC particles at an abrasion pressure of 45 psi, aring-on-ring load-to-failure of at least 80 kgf. β-spodumene solidsolution is hereinafter referred to simply as “0-spodumene.” β-quartzsolid solution is hereinafter referred to simply as “β-quartz.”

According to aspect (1), a method of manufacturing a glass-ceramicarticle is provided. The method comprises: (a) maintaining a precursorglass in an environment for a first time period of 1.75 to 4.25 hourswhile the environment has a first temperature of 590° C. to 820° C., theprecursor glass having a composition comprising, on an oxide basis:55-75 mol % SiO₂; 0.2-10 mol % Al₂O₃; 0-5 mol % B₂O₃; 15-30 mol % Li₂O;0-2 mol % Na₂O; 0-2 mol % K₂O; 0-5 mol % MgO; 0-2 mol % ZnO; 0.2-3.0 mol% P₂O₅; 0.1-10 mol % ZrO₂; 0-4 mol % TiO₂; and 0-1.0 mol % SnO₂; (b)maintaining the precursor glass in the environment for a second timeperiod of 0.75 hour to 4.25 hours while the environment has a secondtemperature of 850° C. to 925° C., forming a glass-ceramic substrate,wherein (i) lithium disilicate and (ii) either β-spodumene or β-quartzare the two predominant crystalline phases by weight percentage of theglass-ceramic substrate, and wherein tetragonal ZrO₂ is a crystallinephase of the glass-ceramic substrate; and (c) subjecting theglass-ceramic substrate to an ion-exchange treatment in a molten saltbath that comprises a salt of one or more of ionic Na, K, and Ag,forming a glass-ceramic article; wherein at least one of the followingconditions is true: (i) the composition of the precursor glass wascharacterized by Na₂O+K₂O≤0.5 mol %, but sodium ions are presentthroughout an entire thickness of the glass-ceramic article; (ii) thecomposition of a portion of the glass-ceramic article from a primarysurface into the thickness comprises over 10 mol % Na₂O, on an oxidebasis; (iii) the bath of the ion-exchange treatment comprises greaterthan 98 percent by weight NaNO₃ and 0.01 to 1 percent by weight LiNO₃;and the mole percentage of Na₂O within the glass-ceramic articledecreases as a function of depth into the thickness of the glass-ceramicarticle from the primary surface, with the maximum mole percentage ofNa₂O at any depth being 7 mol % Na₂O, and sodium ions are present withinthe glass-ceramic article to a depth of at least 15 percent of thethickness from the primary surface; and (iv) the ion-exchange treatmentcomprises a first ion-exchange treatment in which a first bath comprisesat least 98 percent by weight NaNO₃ and a second ion-exchange step inwhich a second bath comprises ions of potassium or silver; and (i) afirst portion of the thickness of the glass-ceramic article comprises amole percentage of either K₂O or Ag₂O that is greater than the molepercentage of Na₂O and (ii) a second portion of the thickness of theglass-ceramic article comprises a mole percentage of Na₂O that isgreater than the mole percentage of either K₂O or Ag₂O.

According to aspect (2), the method of aspect (1) is provided, wherein:the precursor glass was characterized by Na₂O+K₂O≤0.5 mol %, but sodiumions are present throughout the entire thickness of the glass-ceramicarticle.

According to aspect (3), the method of aspect (1) is provided, wherein:the composition of a portion of the glass-ceramic article from theprimary surface into the thickness comprises over 10 mol % Na₂O, on anoxide basis.

According to aspect (4), the method of aspect (1) is provided, whereinthe bath of the ion-exchange treatment comprises greater than 98 percentby weight NaNO₃ and 0.01 to 1 percent by weight LiNO₃; and the molepercentage of Na₂O within the glass-ceramic article decreases as afunction of depth into the thickness of the glass-ceramic article fromthe primary surface, with the maximum mole percentage of Na₂O at anydepth being 7 mol % Na₂O, and sodium ions are present within theglass-ceramic article to a depth of at least 15 percent of the thicknessfrom the primary surface.

According to aspect (5), the method of aspect (1) is provided, wherein:the ion-exchange treatment comprises the first ion-exchange treatment inwhich the first bath comprises at least 98 percent by weight NaNO₃ andthe second ion-exchange step in which the second bath comprises ions ofpotassium or silver; and (i) the first portion of the thickness of theglass-ceramic article comprises a mole percentage of either K₂O or Ag₂Othat is greater than the mole percentage of Na₂O and (ii) the secondportion of the thickness of the glass-ceramic article comprises a molepercentage of Na₂O that is greater than the mole percentage of eitherK₂O or Ag₂O.

According to aspect (6), the method of any of aspects (1) to (5) isprovided, wherein: the precursor glass was substantially free of Na₂O.

According to aspect (7), the method of any of aspects (1) to (5) isprovided, wherein: the first temperature is in the range of 590° C. to770° C.

According to aspect (8), the method of any of aspects (1) to (7) isprovided, wherein: the glass-ceramic substrate has a fracture toughnessof 1.0 to 3.0 MPa·m^(1/2).

According to aspect (9), the method of any of aspects (1) to (8) isprovided, wherein: the thickness of the glass-ceramic article is 0.3 mmto 2.0 mm.

According to aspect (10), the method of aspect (9) is provided, wherein:the glass-ceramic article exhibits a ring-on-ring load-to-failure of atleast 120 kgf.

According to aspect (11), the method of aspect (9) or (10) is provided,after being abraded with SiC particles at an abrasion pressure of 45psi, the glass-ceramic article exhibits a ring-on-ring load-to-failureof at least 80 kgf.

According to aspect (12), the method of any of aspects (1) to (11) isprovided, wherein: the glass-ceramic substrate exhibits a color, underan F02 illuminant, presented in CIELAB color space coordinates: L*=88 to98; a*=−1.0 to 1; and b*=−4.0 to 4.0.

According to aspect (13), the method of any of aspects (1) to (12) isprovided, wherein: the composition of the precursor glass comprises, onan oxide basis: 68.6-71.5 mol % SiO₂; 1.0-4.5 mol % Al₂O₃; 21.5-22.2 mol% Li₂O; 0.7-1.2 mol % P₂O₅; 1.5-5.0 mol % ZrO₂; and 0-1.0 mol % SnO₂,wherein the precursor glass is substantially free of B₂O₃; Na₂O; K₂O;MgO; ZnO; and TiO₂.

According to aspect (14), the method of any of aspects (1) to (13) isprovided, wherein: the composition of the precursor glass comprises, onan oxide basis: 68.6-70.9 mol % SiO₂; 1.0-4.3 mol % Al₂O₃; 21.5-22.2 mol% Li₂O; 0.9-1.2 mol % P₂O₅; 2.0-5.0 mol % ZrO₂; and 0-1.0 mol % SnO₂,wherein the precursor glass is substantially free of B₂O₃; Na₂O; K₂O;MgO; ZnO; and TiO₂.

According to aspect (15), the method of any of aspects (1) to (14) isprovided, wherein: the glass-ceramic substrate has a fracture toughnessof 1.4 to 2.4 MPa·m^(1/2).

According to aspect (16), the method of any of aspects (1) to (15) isprovided, wherein:

the glass-ceramic substrate exhibits a color, under an F02 illuminant,presented in CIELAB color space coordinates: L*=93 to 97; a*=−1.0 to 0;and b*=−1.0 to 3.0.

According to aspect (17), the method of any of aspects (1) to (16) isprovided, wherein:

the glass-ceramic substrate has an average opacity of 79 to 96 percentthroughout the wavelength range of 400 nm to 700 nm for a thickness of0.8 mm.

According to aspect (18), the method of any of aspects (1) to (17) isprovided, wherein:

the precursor glass comprises 3.4 mol % to 4.3 mol % Al₂O₃; and lithiumdisilicate and β-spodumene are the two predominant crystalline phases byweight of the glass-ceramic article.

According to aspect (19), the method of any of aspects (1) to (5) and(7) to (12) is provided, wherein: the precursor glass comprises, on anoxide basis: 70.0-70.6 mol % SiO₂; 4.85-4.95 mol % Al₂O₃; 19.2-19.4 mol% Li₂O; 0.195-0.205 mol % Na₂O; 0.9-1.1 mol % P₂O₅; 1.8-2.6 mol % ZrO₂;1.9-2.1 mol % TiO₂; and 0.09-0.11 mol % SnO₂, wherein the precursorglass is substantially free of B₂O₃; K₂O; MgO; and ZnO; and β-spodumeneand lithium disilicate are the two predominant crystalline phases byweight of the glass-ceramic article.

According to aspect (20), the method of aspect (19) is provided,wherein: the glass-ceramic article further comprises rutile as acrystalline phase.

According to aspect (21), a glass-ceramic substrate is provided. Theglass-ceramic substrate comprises: a composition comprising, on an oxidebasis: 68.6-71.5 mol % SiO₂; 1.0-4.5 mol % Al₂O₃; 21.5-22.2 mol % Li₂O;0.7-1.2 mol % P₂O₅; 1.5-5.0 mol % ZrO₂; and 0-1.0 mol % SnO₂; wherein(i) lithium disilicate and (ii) either β-spodumene or β-quartz are thetwo predominant crystalline phases by weight percentage of theglass-ceramic substrate; and wherein tetragonal ZrO₂ is a crystallinephase of the glass-ceramic substrate.

According to aspect (22), the glass-ceramic substrate of aspect (21) isprovided, comprising: 68.6-70.9 mol % SiO₂; 1.0-4.3 mol % Al₂O₃; 0.9-1.2mol % P₂O₅; and 3.0-5.0 mol % ZrO₂.

According to aspect (23), the glass-ceramic substrate of any of aspects(21) to (22) is provided, wherein: the composition of the glass-ceramicsubstrate is substantially free of B₂O₃; Na₂O; K₂O; MgO; TiO₂; and ZnO.

According to aspect (24), the glass-ceramic substrate of any of aspects(21) to (23) is provided, wherein: the glass-ceramic substrate has afracture toughness greater than or equal to 2.2 MPa·m^(1/2).

According to aspect (25), a glass-ceramic article is provided. Theglass-ceramic article comprises: a composition at a center-volumecomprising, on an oxide basis: 55-75 mol % SiO₂; 0.2-10 mol % Al₂O₃; 0-5mol % B₂O₃; 15-30 mol % Li₂O; 0-2 mol % Na₂O; 0-2 mol % K₂O; 0-5 mol %MgO; 0-2 mol % ZnO; 0.2-3.0 mol % P₂O₅; 0.1-10 mol % ZrO₂; 0-4 mol %TiO₂; and 0-1.0 mol % SnO₂; wherein (i) lithium disilicate and (ii)either β-spodumene or β-quartz are the two predominant crystallinephases (by weight) of the glass-ceramic article; wherein theglass-article further comprises tetragonal ZrO₂ as a crystalline phase;and wherein at least one of the following conditions are true: (i) thecomposition of the glass-ceramic article from a primary surface into athickness of the glass-ceramic article comprises over 10 mol % Na₂O, onan oxide basis, with the mole percentage of Na₂O decreasing from theprimary surface towards the center-volume; and (ii) the mole percentageof Na₂O within the glass-ceramic article decreases as a function ofdepth into the thickness of the glass-ceramic article from the primarysurface, with the maximum mole percentage of Na₂O at any depth being 7mol % Na₂O, and sodium ions are present within the glass-ceramic articleto a depth of at least 15 percent of the thickness from the primarysurface.

According to aspect (26), the glass-ceramic article of aspect (25) isprovided, wherein the composition of the glass-ceramic article from theprimary surface into the thickness of the glass-ceramic articlecomprises over 10 mol % Na₂O, with the mole percentage of Na₂Odecreasing from the primary surface towards the center-volume.

According to aspect (27), the glass-ceramic article of aspect (25) isprovided, wherein the mole percentage of Na₂O within the glass-ceramicarticle decreases as a function of depth into the thickness of theglass-ceramic article from the primary surface, with the maximum molepercentage of Na₂O at any depth being 7 mol % Na₂O and, and sodium ionsare present within the glass-ceramic article to a depth of at least 15percent of the thickness from the primary surface.

According to aspect (28), the glass-ceramic article of any of aspects(25) to (27) is provided, wherein: the thickness of the glass-ceramicarticle is 0.3 mm to 2.0 mm.

According to aspect (29), the glass-ceramic article of aspect (28) isprovided, wherein: the glass-ceramic article exhibits a ring-on-ringload-to-failure of at least 120 kgf.

According to aspect (30), the glass-ceramic article of any of aspects(28) to (29) is provided, wherein after being abraded with SiC particlesat an abrasion pressure of 45 psi, the glass-ceramic article exhibits aring-on-ring load-to-failure of at least 80 kgf.

According to aspect (31), the glass-ceramic article of any of aspects(25) to (30) is provided, wherein: the composition of the glass-ceramicarticle at the center-volume comprises, on an oxide basis: 68.6-71.5 mol% SiO₂; 1.0-4.5 mol % Al₂O₃; 21.5-22.2 mol % Li₂O; 0.7-1.2 mol % P₂O₅;1.5-5.0 mol % ZrO₂; and 0-0.1 mol % SnO₂, wherein the glass-ceramicarticle is substantially free of B₂O₃; MgO; ZnO; and TiO₂.

According to aspect (32), the glass-ceramic article of any of aspects(25) to (31) is provided, wherein: the composition of the glass-ceramicarticle at the center-volume comprises, on an oxide basis: 68.6-70.9 mol% SiO₂; 1.0-4.3 mol % Al₂O₃; 21.5-22.2 mol % Li₂O; 0.9-1.2 mol % P₂O₅;2.0-5.0 mol % ZrO₂; and 0-0.1 mol % SnO₂, wherein the glass-ceramicarticle is substantially free of B₂O₃; MgO; ZnO; and TiO₂.

According to aspect (33), the glass-ceramic article of any of aspects(25) to (32) is provided, wherein: the composition of the glass-ceramicarticle at the center-volume comprises (on an oxide basis): 68.6-70.9mol % SiO₂; 1.0-4.3 mol % Al₂O₃; 21.5-22.2 mol % Li₂O; 0.9-1.2 mol %P₂O₅; 3.0-5.0 mol % ZrO₂; and 0-1.0 mol % SnO₂.

According to aspect (34), the glass-ceramic article of any of aspects(25) to (33) is provided, wherein: the glass-ceramic article exhibits acolor, under an F02 illuminant, presented in CIELAB color spacecoordinates: L*: 93 to 97; a*: −1.0 to 0; and b*: −1.0 to 3.0.

According to aspect (35), the glass-ceramic article of any of aspects(25) to (34) is provided, wherein: the glass-ceramic substrate has anaverage opacity of 79 to 96 percent throughout the wavelength range of400 nm to 700 nm for a thickness of 0.8 mm.

According to aspect (36), the glass-ceramic article of any of aspects(25) to (35) is provided, wherein: the composition of the glass-ceramicarticle at the center-volume comprises, on an oxide basis, 3.4 to 4.3mol % Al₂O₃; and lithium disilicate and β-spodumene are the twopredominant by weight crystalline phases of the glass-ceramic article.

According to aspect (37), the glass-ceramic article of any of aspects(25) to (30) is provided, wherein: the composition of the glass-ceramicarticle at the center-volume comprises, on an oxide basis: 70.0-70.6 mol% SiO₂; 4.85-4.95 mol % Al₂O₃; 19.2-19.4 mol % Li₂O; 0.195-0.205 mol %Na₂O; 0.9-1.1 mol % P₂O₅; 1.8-2.6 mol % ZrO₂; 1.9-2.1 mol % TiO₂; and0.09-0.11 mol % SnO₂, wherein the glass-ceramic article at thecenter-volume is substantially free of B₂O₃; K₂O; MgO; and ZnO; andlithium disilicate and β-spodumene are the two predominant crystallinephases by weight of the glass-ceramic article.

According to aspect (38), the glass-ceramic article of aspect (37) isprovided, wherein: the glass-ceramic article further comprises rutile asa crystalline phase.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring to the drawings in general, it will be understood that theillustrations are for the purpose of describing particular embodimentsand are not intended to limit the disclosure or appended claims thereto.The drawings are not necessarily to scale, and certain features andcertain views of the drawings may be shown exaggerated in scale or inschematic in the interest of clarity and conciseness.

FIG. 1 is a flow and schematic diagram of a method of manufacturing aglass-ceramic article according to embodiments of this disclosure;

FIG. 2 is a perspective view of embodiments of a precursor glass,glass-ceramic substrate, and glass-ceramic article of the presentdisclosure;

FIG. 3 is an elevational view of a cross-section of the precursor glass,glass-ceramic substrate, and glass-ceramic article of FIG. 2 takenthrough line of FIG. 2;

FIG. 4 is a plot of the reflected x-ray diffraction intensities(“Intensity”) as a function of the detector angle (“2 theta (°)”) for anexample glass-ceramic substrate (Example 1E) manufactured pursuant tothe method of FIG. 1, illustrating lithium disilicate and β-spodumene asthe two predominant crystalline phases (by weight percentage) of theglass-ceramic substrate, and also tetragonal ZrO₂ (“t-ZrO₂”) andlithiophosphate as crystalline phases;

FIG. 5A is a scanning electron microscope image of the glass-ceramicsubstrate of FIG. 4 (Example 1E);

FIG. 5B is another scanning electron microscope image of theglass-ceramic substrate of FIG. 4 (Example 1E), illustrating white spotscorresponding to the tetragonal ZrO₂ crystalline phase, needlescorresponding to the lithium disilicate crystalline phase, and greyblocks corresponding to the β-spodumene crystalline phase;

FIG. 6 is a graph characterizing Na₂O as a function of depth into thethickness for three glass-ceramic articles formed from the glass-ceramicsubstrate of Example 1E, each sample using a different ion-exchangetreatment period of time;

FIG. 7 is a Weibull distribution representing the probability of theglass-ceramic substrates of Example 1E failing in response to variousring-on-ring loads (not having undergone ion-exchange treatment pursuantto a step of the method of FIG. 1) versus the probability of theglass-ceramic articles made from the glass-ceramic substrates of Example1E failing (having undergone ion-exchange treatment pursuant to a stepof the method of FIG. 1);

FIG. 8 is a graph of load-to-failure as a function of the pressure atwhich SiC particles abraded samples of the glass-ceramic substrate ofExample 1E, as well as samples of a glass-ceramic substrate of aComparative Example, illustrating the glass-ceramic substrate of Example1E retaining more strength after abrasion (i.e., requiring moreload-to-failure) than the Comparative Example;

FIG. 9 is a graph characterizing Na₂O as a function of depth into thethickness for two glass-ceramic articles formed from the glass-ceramicsubstrate of Example 1, each sample using a different bath compositionfor the ion-exchange treatment, illustrating that, when the bath did notinclude LiNO₃, spikes in the mole percentage as a function of depth intothe thickness were generated near the primary surfaces of theglass-ceramic article, but when the bath did include LiNO₃, no suchspikes occurred;

FIG. 10 is a scanning electron microscope (SEM) image of a glass-ceramicsubstrate according to an embodiment;

FIG. 11 is a SEM image of the glass-ceramic substrate of FIG. 10 at anincreased magnification;

FIG. 12 is a graph of the results of a drop test of glass-ceramicarticles according to embodiments and a comparative example onto 80 gritsandpaper;

FIG. 13 is a graph of the results of a drop test of a glass-ceramicarticle according to embodiments and comparative examples onto 80 gritsandpaper; and

FIG. 14 is a graph of the results of a drop test of glass-ceramicarticles according to embodiments and a comparative example onto 30 gritsandpaper.

DETAILED DESCRIPTION

Referring now to FIGS. 1-3, a method 10 of manufacturing a glass-ceramicarticle 12 is herein described. At a step 14, the method 10 includesmaintaining a precursor glass 16 in an environment 18 for a first timeperiod of 1.75 hours to 4.25 hours while the environment has a firsttemperature of 590° C. to 770° C.

In embodiments, the first temperature is 590° C. to 820° C. Inembodiments, the first temperature is 590° C. to 810° C., 590° C. to800° C., 590° C. to 790° C., 590° C. to 780° C., 590° C. to 770° C.,590° C. to 710° C., 690° C. to 710° C., 625° C. to 770° C., or 750° C.to 770° C. In embodiments, the first temperature is 590° C., 600° C.,610° C., 620° C., 630° C., 640° C., 650° C., 660° C., 670° C., 680° C.,690° C., 700° C., 710° C., 720° C., 730° C., 740° C., 750° C., 760° C.,770° C., 780° C., 790° C., 800° C., 810° C., 820° C., or any rangewithin between any two of those temperatures (e.g., 630° C. to 750° C.,690° C. to 720° C., etc.).

In embodiments, the environment 18 increases in temperature to the firsttemperature before step 14 at a rate of 4° C. to 6° C. per minute (suchas about 5° C. per minute, or 5° C. per minute). For example, if theenvironment 18 is initially at room temperature (e.g., 20° C.), thenafter 1 minute the environment 18 could be 25° C., then after anadditional 1 minute the environment 18 could be 30° C., and so on untilthe environment 18 is at the first temperature. As another example, ifthe environment 18 is initially at room temperature (e.g. 20° C.), thenafter 10 minutes the environment 18 could be 75° C., then after anadditional 10 minutes the environment 18 could be 125° C., and so onuntil the environment 18 is at the first temperature.

In embodiments, the first time period is 1.75 hours to 4.25 hours. Inembodiments, the first time period is 1.75 to 2.25 hours, or 3.75 to4.25 hours. In embodiments, the first time period is 1.75 hours, 2hours, 2.25 hours, 2.5 hours, 2.75 hours, 3 hours, 3.25 hours, 3.5hours, 3.75 hours, 4 hours, or 4.25 hours, or any range including anytwo of those time periods (e.g., 1.75 hour to 3.75 hours, 1.5 hour to 4hours, etc.).

In embodiments, the precursor glass 16 has a thickness 22. Inembodiments, the precursor glass 16 has two primary surfaces 24 a, 24 b.In those embodiments, the thickness 22 is the shortest straight-linedistance between the two primary surfaces 24 a, 24 b. In embodiments,the thickness 22 of the precursor glass 16 is 0.3 mm to 10.0 cm, such as0.3 mm to 2.0 cm, 0.3 mm to 1.0 cm, 0.3 mm to 2.0 mm. In embodiments,the thickness 22 is 0.3 mm, 0.4 mm, 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9mm, 1.0 mm, 1.1 mm, 1.2 mm, 1.3 mm, 1.4 mm, 1.5 mm, 1.6 mm, 1.7 mm, 1.8mm, 1.9 mm, or 2.0 mm, or any range including any two of thosethicknesses (e.g., 0.5 mm to 1.2 mm, 0.6 mm to 1.0 mm, or 0.9 mm to 1.1mm, etc.).

Then, at a step 20, the method 10 further includes maintaining theprecursor glass 16 in the environment 18 for a second time period of0.75 hour to 4.25 hours while the environment 18 has a secondtemperature of 850° C. to 925° C. After at least the step 20, theprecursor glass 16 has transformed into a glass-ceramic substrate 26.The steps 14 and 20 are sometimes collectively referred to as the act ofceramming the precursor glass 16.

In embodiments, the second temperature is 850° C. to 925° C. Inembodiments, the second temperature is 865° C. to 900° C. Inembodiments, the second temperature is 850° C., 860° C., 870° C., 880°C., 890° C., 900° C., 910° C., 920° C., 925° C., or any range includingany two of those temperatures (e.g., 910° C. to 925° C., 890° C. to 920°C., etc.).

In embodiments, the second time period is 0.75 hour to 4.25 hours. Inembodiments, the second time period is 1 hour to 4 hours. Inembodiments, the second time period is 0.75 hour, 1 hour, 1.25 hour,1.50 hour, 1.75 hour, 2 hours, 2.25 hours, 2.5 hours, 2.75 hours, 3hours, 3.25 hours, 3.5 hours, 3.75 hours, 4 hours, 4.25 hours, or anyrange including any two of those time periods (e.g., 1.75 hour to 3.75hours, 1.5 hour to 4 hours, etc.).

When the precursor glass 16 is cerammed into the glass-ceramic substrate26, portions of the glass crystallize while other portions may remain ina residual glass phase (e.g., amorphous, non-crystalline). As usedherein, the term “glass-ceramic” refers to a material comprising atleast one crystalline phase and at least one residual glass phase. Inparticular, the glass-ceramic substrate 26 of this disclosure includes(i) lithium disilicate (Li₂Si₂O₅) and (ii) either β-spodumene orβ-quartz as the two predominant crystalline phases by weight-percentageof the glass-ceramic substrate 26. The glass-ceramic substrate 26 ofthis disclosure further includes tetragonal ZrO₂ as a crystalline phase.In embodiments, one or more of lithiophosphate, β-quartz (if not one ofthe two predominant crystalline phases), rutile, and monoclinic ZrO₂ arepresent as minor crystalline phases of the glass-ceramic substrate 26(i.e., not one of the two predominant crystalline phases). Theglass-ceramic substrate 26 may have the same thickness 22 as theprecursor glass 16, and in embodiments is 0.3 mm to 10.0 cm, such as 0.3mm to 2.0 cm, 0.3 mm to 1.0 cm, 0.3 mm to 2.0 mm. In embodiments, thethickness of the glass-ceramic substrate 26 is 0.3 mm, 0.4 mm, 0.5 mm,0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1.0 mm, 1.1 mm, 1.2 mm, 1.3 mm, 1.4 mm,1.5 mm, 1.6 mm, 1.7 mm, 1.8 mm, 1.9 mm, 2.0 mm, 3.0 mm, 4.0 mm, 5.0 mm,6.0 mm, 2.0 mm, 7.0 mm, 8.0 mm, 9.0 mm, 10.0 mm, 2.0 cm, or 10.0 cm, orany range including any two of those thicknesses (e.g., 0.5 mm to 1.2mm, 0.6 mm to 1.0 mm, or 0.9 mm to 1.1 mm, etc.).

The precursor glass 16, and thus the glass-ceramic substrate 26,providing the basis for the exceptional fracture toughness describedbelow has a composition. The composition comprises (in mole percent ofthe total composition, on an oxide basis): 55-75 mol % SiO₂; 0.2-10 mol% Al₂O₃; 0-5 mol % B₂O₃; 15-30 mol % Li₂O; 0-2 mol % Na₂O; 0-2 mol %K₂O; 0-5 mol % MgO; 0-2 mol % ZnO; 0.2-3.0 mol % P₂O₅; 0.1-10 mol %ZrO₂; 0-4 mol % TiO₂; and 0-1.0 mol % SnO₂. In embodiments, thecomposition comprises: 68.6-71.5 mol % SiO₂; 1.0-4.5 mol % Al₂O₃;21.5-22.2 mol % Li₂O; 0.7-1.2 mol % P₂O₅; 1.5-5.0 mol % ZrO₂; and 0-1.0mol % SnO₂. In embodiments, the composition comprises: 68.6-70.9 mol %SiO₂; 1.0-4.3 mol % Al₂O₃; 21.5-22.2 mol % Li₂O; 0.9-1.2 mol % P₂O₅;2.0-5.0 mol % ZrO₂; and 0-1.0 mol % SnO₂. In some cases, the compositioncomprises 3.4 mol % to 4.3 mol % Al₂O₃. In some cases, the compositioncomprises 3.4 mol % to 4.3 mol % Al₂O₃. In some cases, the compositioncomprises 68.6-70.9 mol % SiO₂; 1.0-4.3 mol % Al₂O₃; 21.5-22.2 mol %Li₂O; 0.9-1.2 mol % P₂O₅; 3.0-5.0 mol % ZrO₂; and 0-1.0 mol % SnO₂. Inembodiments, the composition comprises: 70.0-70.6 mol % SiO₂; 4.85-4.95mol % Al₂O₃; 19.2-19.4 mol % Li₂O; 0.195-0.205 mol % Na₂O; 0.9-1.1 mol %P₂O₅; 1.8-2.6 mol % ZrO₂; 1.9-2.1 mol % TiO₂; and 0.09-0.11 mol % SnO₂.For purposes of this disclosure, composition ranges are inclusive ofstated endpoints. For example, 55-75 mol % SiO₂ means that the molepercentage of SiO₂ in the composition is greater than or equal to 55 mol% and less than or equal to 75 mol %—in other words, 55 mol %≤mol %SiO₂≤75 mol %.

In embodiments, the composition is substantially free or free of B₂O₃.In embodiments, the composition includes a total amount of Na₂O+K₂O ofless than or equal to 0.5 mol %. In embodiments, the composition issubstantially free or free of Na₂O. In embodiments, the composition issubstantially free or free of K₂O. In embodiments, the composition issubstantially free or free of MgO. In embodiments, the composition issubstantially free or free of ZnO. In embodiments, the composition issubstantially free or free of TiO₂. In some cases, the composition issubstantially free or free of all of B₂O₃; K₂O; MgO; and ZnO. Inembodiments, the composition is substantially free or free of all ofB₂O₃; Na₂O; K₂O; MgO; ZnO; and TiO₂. “Substantially free” means that thecomponent is not actively added, batched, or included into thecomposition, but may be present in very small amounts as a contaminant(e.g., 500 parts per million (ppm) or less).

SiO₂ serves as the primary glass-forming oxide for the precursor glass16 and can function to stabilize the networking structure of theprecursor glass 16 and the glass-ceramic substrate 26. The precursorglass 16 and the glass-ceramic substrate 26 comprise 55-75 mol % SiO₂.In embodiments, the composition comprises 68.6-71.5 mol % SiO₂, such as68.6-70.9 mol % SiO₂. In embodiments, the composition comprises70.0-70.6 mol % SiO₂. In embodiments, the composition comprises 55, 56,57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 68.6, 69, 70, 70.9, 71,72, 73, 74, or 75 mol % SiO₂, or any range including any two of thosemole percentages (e.g., 57-69 mol % SiO₂, 63-73 mol % SiO₂, etc.). Thecontent of SiO₂ is at least 55 mol % so that lithium disilicate(Li₂Si₂O₅) and either β-spodumene or β-quartz are the two predominantcrystalline phases when the precursor glass 16 is heat treated toconvert to the glass-ceramic substrate 26. The amount of SiO₂ is limitedto 75 mol % to control melting temperature, because the meltingtemperature of pure SiO₂ or high-SiO₂ glasses is undesirably high.

Al₂O₃ may also provide stabilization to the network and is an essentialconstituent in the β-spodumene crystalline phase. Al₂O₃ may increase theviscosity of the precursor glass compositions used to form the glassceramics due to its tetrahedral coordination in a glass melt formed froma glass composition, decreasing the formability of the glass compositionwhen the amount of Al₂O₃ is too high. However, when the concentration ofAl₂O₃ is balanced against the concentration of SiO₂ and theconcentration of alkali oxides in the glass composition, Al₂O₃ canreduce the liquidus temperature of the glass melt, thereby enhancing theliquidus viscosity and improving the compatibility of the glasscomposition with certain forming processes, such as the fusion formingprocess. In addition, the presence of Al₂O₃ in the composition isfavorable to an improvement of mechanical properties and chemicaldurability of the precursor glass 16 and glass-ceramic substrate 26.However, if the amount of Al₂O₃ is too high, then the fraction oflithium disilicate crystals may be decreased, possibly to the extentthat an interlocking structure cannot be formed. In embodiments, thecomposition comprises 0.2-10 mol % Al₂O₃. In embodiments, thecomposition comprises 1.0-4.5 mol % Al₂O₃, such as 1.0-4.3 mol % Al₂O₃.In embodiments, the composition comprises 3.4-4.3 mol % Al₂O₃. Inembodiments, the composition comprises 4.85-4.95 mol % Al₂O₃. Inembodiments, the composition comprises 0.2, 0.5, 1.0, 1.5, 2.0, 2.5,3.0, 3.4, 3.5, 4, 4.3, 4.5, 4.85, 4.95, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5,9, 9.5, or 10 mol % Al₂O₃, or any range including any two of those molepercentages (e.g., 4.5-7.5 mol % Al₂O₃, 5-9.5 mol % Al₂O₃, etc.).

B₂O₃, if included in the composition, can be conducive to lowering themelting temperature of the precursor glass 16. Furthermore, the additionof B₂O₃ in the composition helps achieve an interlocking crystalmicrostructure and improve the damage resistance of the glass-ceramicsubstrate 26. Moreover, the presence of B₂O₃ in the composition lowersthe viscosity of the precursor glass 16, which facilitates the growth oflithium disilicate crystals, especially large crystals having a highaspect ratio. However, the amount of B₂O₃ in general should be limitedto maintain chemical durability and mechanical strength of theglass-ceramic substrate 26. In embodiments, the composition comprises0-5 mol % B₂O₃. In embodiments, the composition comprises 0, 0.5, 1.0,1.5, 2.0, 2.5, 3.0, 3.5, 4, 4.5, or 5 mol % B₂O₃, or any range includingany two of those mole percentages (e.g., 0.5-2.5 mol % B₂O₃, 2-4.5 mol %B₂O₃, etc.).

Li₂O is required in the composition to form both the lithium disilicatecrystalline phase and the β-spodumene crystalline phase, if desired. ALiO₂ content of 15 mol % in the composition is sufficient to form thelithium disilicate crystalline phase and the β-spodumene crystallinephase, if desired. Without being bound by theory, it is believed thatthe lithium disilicate crystalline phase is at least partiallyresponsible for the improved fracture toughness values described herein.In addition, the composition including at least 15 mol % LiO₂ providessufficient lithium ions to allow for ion-exchange of the glass-ceramicsubstrate 26 as further discussed herein. However, when Li₂O contentgets too high, over 30 mol %, the precursor glasses become very fluidwith low resistivity making it difficult to melt or form. Inembodiments, the composition comprises 15-30 mol % Li₂O. In embodiments,the composition comprises 21.5-22.2 mol % Li₂O. In embodiments, thecomposition comprises 19.2-19.4 mol % Li₂O. In embodiments, thecomposition comprises 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26,27, 28, 29, or 30 mol % Li₂O, or any range including any two of thosemole percentages (e.g., 17-28 mol % Li₂O, 19-29 mol % Li₂O, etc.).

The non-lithium alkali oxides Na₂O and K₂O can be included in thecomposition to reduce the melting temperature of the precursor glass 16,to shorten the ceramming cycle as well, and to reduce cracks associatedwith ceramming by lowering the viscosity of the residual glass phase.However, Na₂O and K₂O tend to drive the presence of aluminosilicateresidual glass in the glass-ceramic substrate 26, which can lead todeformation during crystallization and undesirable microstructures froma mechanical property perspective. In addition, if too much Na₂O isadded to the composition, then the coefficient of thermal expansion ofthe precursor glass 16 and glass-ceramic substrate 26 may be too high.In embodiments, the composition comprises a total content of Na₂O+K₂O ofless than or equal to 0.5 mol %, such as less than or equal to 0.4 mol%, 0.3 mol %, 0.2 mol %, 0.1 mol %, or less. In embodiments, thecomposition comprises 0-2 mol % Na₂O and 0-2 mol % K₂O. In embodiments,the composition comprises 0.195-0.205 mol % Na₂O. In embodiments, thecomposition is substantially free or free of Na₂O, K₂O, or both. Inembodiments, the composition comprises 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6,0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, or 2.0mol % Na₂O, or any range including any two of those mole percentages(e.g., 0.4-1.3 mol % Na₂O, 0.8-1.8 mol % Na₂O, etc.). In embodiments,the composition comprises 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8,0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, or 2.0 mol % K₂O,or any range including any two of those mole percentages (e.g., 0.4-1.3mol % K₂O, 0.8-1.8 mol % K₂O, etc.).

The composition can include MgO and/or ZnO. MgO and ZnO act as a flux,which lowers the cost of production of the precursor glass 16. Thepresence of MgO in the composition may increase the elastic modulus,which can be a desirable property. Both MgO and ZnO may enterβ-spodumene crystals in partial solid solution. In embodiments, thecomposition comprises 0-5 mol % MgO. In embodiments, the compositioncomprises 0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, or 5.0 mol %MgO, or any range including any two of those mole percentages (e.g.,0-3.5 mol % MgO, 1.0-4.5 mol % MgO, etc.). In embodiments, thecomposition is substantially free or free of MgO. In embodiments, thecomposition comprises 0-2 mol % ZnO. In embodiments, the compositioncomprises 0, 0.5, 1.0, 1.5, or 2.0 mol % ZnO, or any range including anytwo of those mole percentages (e.g., 0-1.5 mol % ZnO, 1.0-2.0 mol % ZnO,etc.). In embodiments, the composition is substantially free or free ofZnO.

The composition includes P₂O₅. P₂O₅ serves as a nucleating agent toproduce bulk nucleation. If the concentration of P₂O₅ is too low, theprecursor glass 16 does not crystallize or undergoes surfacecrystallization which is unwanted. If the concentration of P₂O₅ is toohigh, devitrification of the precursor glass 16 upon cooling duringforming may be difficult to control. The presence of P₂O₅ in the glassceramic substrate 26 may also increase the diffusivity of metal ions inthe glass ceramic, which may increase the efficiency of ion exchangingthe glass ceramic substrate 26. In embodiments, the compositioncomprises 0.2-3.0 mol % P₂O₅. In embodiments, the composition comprises0.7-1.2 mol % P₂O₅, such as 0.9-1.2 mol % P₂O₅. In embodiments, thecomposition comprises 0.9-1.1 mol % P₂O₅. In embodiments, thecomposition comprises 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1,1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5,2.6, 2.7, 2.8, 2.9, or 3.0 mol % P₂O₅, or any range including any two ofthose mole percentages (e.g., 0.4-1.5 mol % P₂O₅, 1.0-2.8 mol % P₂O₅,etc.).

The composition includes ZrO₂. ZrO₂ acts as a network former orintermediate in the precursor glass 16 and is a necessary component forthe formation of the tetragonal ZrO₂ crystalline phase in theglass-ceramic. In addition, ZrO₂ can improve the stability ofLi₂O—Al₂O₃—SiO₂—P₂O₅ glass by significantly reducing glassdevitrification during forming and lowering liquidus temperature. Inaddition, the presence of crystalline ZrO₂ phase in the glass substrate26 is beneficial for achieving bright white color with high opacity.Further, the addition of ZrO₂ is believed to increase the chemicaldurability of the glass-ceramic substrate 26, and can increase theelastic modulus of the residual glass phase in the glass-ceramicsubstrate 26, which can be desirable. ZrO₂ is the primary component ofthe tetragonal ZrO₂ crystalline phase. In embodiments, the compositionincludes 0.1-10 mol % ZrO₂. In embodiments, the composition includes1.5-5.0 mol % ZrO₂, such as 2.0-5.0 mol % ZrO₂. In embodiments, thecomposition comprises 3.0-5.0 mol % ZrO₂. In embodiments, thecomposition comprises 1.8-2.6 mol % ZrO₂. In embodiments, thecomposition comprises 0.1, 0.5, 1.0, 1.5, 1.8, 2.0, 2.5, 2.6, 3.0, 3.5,4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, 9.0, 9.5, or 10.0 mol% ZrO₂, or any range including any two of those mole percentages (e.g.,1.5-7.0 mol % ZrO₂, 5.5-9.5 mol % ZrO₂).

The composition can include TiO₂. The composition can include TiO₂ toprovide the glass-ceramic substrate 26 with a dense white or creamcolor, and a specific opacity. Where TiO₂ is utilized, the resultingglass-ceramic substrate 26 may also include a minor rutile crystallinephase. The presence of TiO₂ in the recited amount can make theglass-ceramic substrate 26 more opaque and can make the glass-ceramicsubstrate 26 exhibit a different white color than if the glass-ceramicsubstrate 26 did not include TiO₂. In addition, TiO₂ can improve thefracture toughness of the glass-ceramic substrate 26. Further, TiO₂ canact as a nucleating agent for β-spodumene. In embodiments, thecomposition comprises 0-4 mol % TiO₂. In embodiments, the compositioncomprises 1.9-2.1 mol % TiO₂. In embodiments, the composition issubstantially free or free of TiO₂. In embodiments, the compositioncomprises 0, 0.5, 1.0, 1.5, 1.9, 2.0, 2.1, 2.5, 3.0, 3.5, or 4.0 mol %TiO₂ or any range including any two of those mole percentages (e.g.,0.5-3.0 mol % TiO₂, 2.5-3.5 mol % TiO₂).

The composition can include CaO. In embodiments, the compositioncomprises 0-5 mol % CaO, such as 0.5-4.5 mol %, 1.0-4.0 mol %, 1.5-3.5mol %, 2.0-3.0 mol %, 2.5-5 mol %, or any range including any two ofthose mole percentages. In embodiments, the composition is substantiallyfree or free of CaO.

The composition can include SrO. In embodiments, the compositioncomprises 0-5 mol % SrO, such as 0.5-4.5 mol %, 1.0-4.0 mol %, 1.5-3.5mol %, 2.0-3.0 mol %, 2.5-5 mol %, or any range including any two ofthose mole percentages. In embodiments, the composition is substantiallyfree or free of SrO.

The composition can include BaO. In embodiments, the compositioncomprises 0-5 mol % BaO, such as 0.5-4.5 mol %, 1.0-4.0 mol %, 1.5-3.5mol %, 2.0-3.0 mol %, 2.5-5 mol %, or any range including any two ofthose mole percentages. In embodiments, the composition is substantiallyfree or free of BaO.

The composition can include SnO₂. The composition can include SnO₂either as a result of Joule melting using tin-oxide electrodes, throughthe batching of tin containing materials, e.g., SnO₂, SnO, SnCO₃,SnC₂O₂, etc., or through addition of SnO₂ as an agent to adjust variousphysical, melting, color, or forming attributes. SnO₂ can additionallyact as a fining agent. In embodiments, the composition comprises 0-1.0mol % SnO₂. In embodiments, the composition comprises 0.09-0.11 mol %SnO₂. In embodiments, the composition is substantially free or free ofSnO₂. In embodiments, the composition comprises 0, 0.01, 0.02, 0.03,0.04, 0.05, 0.06, 0.07, 0.08, 0.09 0.10, 0.11, 0.12, 0.13, 0.14, 0.150.2, 0.25 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8,0.85, 0.9, 0.95, or 1.0 mol % SnO₂, or any range including any two ofthose mole percentages (e.g., 0.05-0.55 mol % SnO₂, 0.35-0.7 mol %SnO₂).

In embodiments, the precursor glass 16 has an internal liquidustemperature of greater than 900° C., such as greater than 1030° C., suchas 1050° C. to 1300° C., or 1100° C. to 1290° C. In embodiments, theinternal liquidus temperature of the precursor glass 16 is 900° C., 950°C., 1000° C., 1030° C., 1050° C., 1100° C., 1150° C., 1200° C., 1250°C., 1290° C., 1300° C., 1350° C., or 1400° C., or any range includingany two of those temperatures (e.g., 950° C. to 1290° C., or 1100° C. to1350° C. The internal liquidus temperature here is measured by placingcrushed particles of the precursor glass 16 in a platinum boat, placingthe boat in a furnace having a region of gradient temperatures, heatingthe boat in an appropriate temperature region for 24 hours, anddetermining by means of microscopic examination the highest temperatureat which crystals appear in the interior of the precursor glass 16.

In embodiments, the precursor glass 16 has a liquidus viscosity of 400poise to 8000 poise, such as 800 poise to 6000 poise, 580 poise to 5500poise, 880 poise to 5400 poise, 1100 poise to 5500 poise, 1140 poise to5400 poise, 1100 poise to 3000 poise, 1140 poise to 2850 poise, 800poise to 3000 poise, 880 poise to 2850 poise, 800 poise to 1200 poise,or 880 poise to 1140 poise. In embodiments the liquidus viscosity of theprecursor glass is 400 poise, 500 poise, 580 poise, 600 poise, 700poise, 800 poise, 880 poise, 900 poise, 1000 poise, 1100 poise, 1100poise, 1140 poise, 1200 poise, 1300 poise, 1400 poise, 1500 poise, 1600poise, 1700 poise, 1800 poise, 1900 poise, 2000 poise, 2100 poise, 2200poise, 2300 poise, 2400 poise, 2500 poise, 2600 poise, 2700 poise, 2800poise, 2850 poise, 2900 poise, 3000 poise, 3250 poise, 3500 poise, 3750poise, 4000 poise, 4250 poise, 4500 poise, 4750 poise, 5000 poise, 5250poise, 5400 poise, 5500 poise, 6000 poise, 6500 poise, 7000 poise, 7500poise, or 8000 poise, or any range including any two of those values(e.g., 900 poise to 4250 poise, 1200 poise to 3000 poise, etc.). Theliquidus viscosity is the viscosity of the precursor glass 16 at theliquidus temperature. In embodiments, the precursor glass 16 has zirconas the liquidus phase. The liquidus phase is the crystalline phase(s)materializing at the liquidus temperature. In general, a lower internalliquidus temperature and a higher liquidus viscosity are preferred forforming the precursor glass 16.

As mentioned, the glass-ceramic substrate 26 of this disclosure includes(i) lithium disilicate (Li₂Si₂O₅) and (ii) either β-spodumene orβ-quartz as the two predominant crystalline phases by weight-percentageof the glass-ceramic substrate 26. Lithium disilicate is an orthorhombiccrystal based on corrugated sheets of Si₂O₅ tetrahedral arrays. Thecrystals are typically tabular or lath-like in shape, with pronouncedcleavage planes. The crystals interlock in random orientations creatingmicrostructures that, without being bound by theory, impart highfracture toughness and high body toughness to the glass-ceramicsubstrate 26. The randomly-oriented interlocked crystals force cracks topropagate through the material via tortuous paths around these crystals.

β-spodumene, also known as stuffed keatite, possesses a frameworkstructure of corner-connected SiO₄ and AlO₄ tetrahedra that forminterlocking rings. While the β-spodumene formula is often given asLiAlSi₂O₆, the crystal can accommodate a wide range of solid solutiontoward silica, encompassing Li₂O.Al₂O₃.nSiO₂ with n from 4 to 9, or fromless than 60 to almost 80 wt % SiO₂. β-spodumene crystals possess verylow thermal expansion because as temperature increases, their c-axisexpands while their a and b axes contract. As a result, glass-ceramicsbased on β-spodumene are useful technologically in applicationsrequiring good thermal shock resistance. β-quartz also has low thermalexpansion and has fine grain size, but has higher translucency. Whetherceramming results in the glass-ceramic 26 having β-spodumene or β-quartzas one of the two predominant crystalline phases may depend on therelative mole percentage of Al₂O₃ in the composition, with greateramounts of Al₂O₃ resulting in β-spodumene and lesser amounts of Al₂O₃resulting in β-quartz.

Tetragonal ZrO₂ imparts white color to the glass-ceramic substrate 26,as well as a high degree of strength and toughness. The tetragonal ZrO₂phase transforms to the monoclinic phase under mechanical stress, whichleads to transformational toughening and prevents crack formation andpropagation. In embodiments, the crystals of tetragonal ZrO₂ have agreatest dimension of 0.1 μm to 10 μm, such as 0.3 μm to 7 μm, 0.5 μm to4 μm, 0.5 μm to 3 μm, an 0.5 μm to 2.0 μm. In embodiments, the crystalsof tetragonal ZrO₂ have a greatest dimension of 0.1 μm, 0.2 μm, 0.3 μm,0.4 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm,5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, or10 μm, or any range including any two of those values (e.g., 0.2 μm to6.5 μm, or 1 μm to 7.5 μm, etc.).

In embodiments, the glass-ceramic substrate 26 has a fracture toughnessof 1.0 to 3.0 MPa·m^(1/2). In embodiments, the glass-ceramic substrate26 has a fracture toughness of 1.4 to 2.4 MPa·m^(1/2). In embodiments,the glass-ceramic substrate 26 has a fracture toughness greater than orequal to 2.2 MPa·m^(1/2), such as 2.2 MPa·m^(1/2) to 3.0 MPa·m^(1/2), or2.2 MPa·m^(1/2) to 2.4 MPa·m^(1/2). Fracture toughness is measured byChevron notch short bar methods (known in the art and described in ASTMprocedure E1304-97, which is incorporated herein by reference). The testmethod involves application of a load to the mouth of a chevron-notchedspecimen to induce an opening displacement of the specimen mouth.Fracture toughness measured according to this method is relative to aslowly advancing steady-state crack initiated at a chevron notch andpropagating in a chevron-shaped ligament. The fracture toughness isdetermined for the glass-ceramic substrate 26 that has not beenion-exchanged to form a glass-ceramic article 12. Without being bound bytheory, glass-ceramic substrates 26 with high fracture toughness canprovide resistance to crack penetration and improved drop performance.When such glass-ceramic substrates 26 are chemically strengthened, forexample through ion exchange, into the glass-ceramic article 12, theresistance to crack penetration and drop performance can be furtherenhanced. And the high fracture toughness can also increase the amountof stored tensile energy and maximum central tension that can beimparted to the glass-ceramic through chemical tempering whilemaintaining desirable fragmentation of the glass-ceramic article 12 uponfracture. Resistance to crack penetration and high drop performancemetrics are useful attributes for the glass-ceramic substrate 26 andglass-ceramic article 12 applied to devices, such as smart phones, thatare prone to being dropped.

In embodiments, either or both of the glass-ceramic substrate 26 andglass-ceramic article 12 are substantially opaque and have a color thatis substantially white. Substantially white and opaque glass-ceramicsubstrates 26 and glass-ceramic articles 12 provide aesthetic benefitsfor dental, architectural, kitchen appliance, and consumer electronicapplications. For example, it is often aesthetically desirable for theglass-ceramic substrate 26 or glass-ceramic article 12 backing of asmart phone to be substantially opaque and white because it isaesthetically pleasing and obscures the electronic components beneaththe backing within the smart phone.

As used herein, the term “substantially white” means that theglass-ceramic substrate 26 or glass-ceramic article 12, as the case maybe, has a color presented in CIELAB color space coordinates: L*=85 to100; a*=−2 to 8; and b*=−70 to 30. In embodiments, the glass-ceramicsubstrate 26 or glass-ceramic article exhibits a color in CIELAB colorspace coordinates: L*=88 to 98; a*=−1.0 to 1; and b*=−4.0 to 4.0. Inembodiments, the glass-ceramic substrate 26 or glass-ceramic article 12exhibits a color in CIELAB color space coordinates: L*=93 to 97; a*=−1.0to 0; and b*=−1.0 to 3.0. In embodiments, the CIELAB color spacecoordinate L* of the glass-ceramic substrate 26 or glass-ceramic article12 is 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, or100, or any range including any two of those values (e.g, 87 to 96, 92to 98, etc.). In embodiments, the CIELAB color space coordinate a* ofthe glass-ceramic substrate 26 or glass-ceramic article 12 is −2, −1.9,−1.8, −1.7, −1.6, −1.5, −1.4, −1.3, −1.2, −1.1, −1.0, −0.9, −0.8, −0.7,−0.6, −0.5, −0.4, −0.3, −0.2, −0.1, 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6,0.7, 0.8, 0.9, or 1.0, or any range including any two of those values(e.g., −1.9 to 0, 0.2 to 0.8, etc.). In embodiments, the CIELAB colorspace coordinate b* of the glass-ceramic substrate 26 or glass-ceramicarticle 12 is −4, −3.75, −3.5, −3.25, −3.0, −2.75, −2.5, −2.25, −2.0,−1.75, −1.5, −1.25, −1.0, −0.75, −0.5, −0.25, 0, 0.25, 0.5, 0.75, or1.0, or any range including any two of those values (e.g., −3.5 to 0.5,−1.0 to 0.75, etc.). The CIELAB color space coordinates can bedetermined by methods known to those in the art using a Color i7Spectrophotometer (X-Rite Incorporated, Grand Rapids, Mich., USA) usingan F02 illuminant under SCI UVC condition.

As used herein, the term “substantially opaque” means that theglass-ceramic substrate 26 or glass-ceramic article 12, as the case maybe, has an average opacity of 75 percent to 100 percent throughout thewavelength range of 400 nm to 700 nm for 0.8 mm in thickness 22. Inembodiments, the glass-ceramic substrate 26 or glass-ceramic article 12has an average opacity of 79 percent to 100 percent throughout thewavelength range of 400 nm to 700 nm for 0.8 mm in thickness 22, such as79 percent to 96 percent. In embodiments, throughout the wavelengthrange of 400 nm to 700 nm for 0.8 mm in thickness 22, the glass-ceramicsubstrate 26 or the glass-ceramic article 12 has an average opacity of75 percent, 76 percent, 77 percent, 78 percent, 79 percent, 80 percent,anyone percent, 81 percent, 82 percent, 83 percent, 84 percent, 85percent, 86 percent, 87 percent, 88 percent, 89 percent, 90 percent, 91percent, 92 percent, 93 percent, 94 percent, 95 percent, 96 percent, 97percent, 98 percent, 99 percent, or 100 percent, or any range includingany two of those values (e.g., 83 percent to 91 percent, 88 percent to99 percent etc.). Average opacity can be determined using the contrastmethod with the Color i7 Spectrophotometer.

At a step 28, the method 10 further comprises subjecting theglass-ceramic substrate 26 to an ion-exchange treatment in a bath 30,transforming the glass-ceramic substrate 26 into the glass-ceramicarticle 12. The term “ion exchange” means treating the glass-ceramicsubstrate 26 with a heated solution containing ions having a differentionic radius than ions that are present within the glass-ceramicsubstrate 26, thus replacing those ions with smaller ions with thelarger ions or vice versa depending on the temperature conditions of thebath 30. For example, lithium ions within the glass-ceramic substrate 26can be replaced by larger sodium, potassium or silver atoms (among otheroptions) from the bath 30. Alternatively, other alkali metal ions havinglarger atomic radii, such as (Rb) rubidium or cesium (Cs) could replacesmaller alkali metal ions in the glass-ceramic substrate 26.

The glass-ceramic article 12 includes a residual glass phase (that is,glass that did not crystalize during the heat treatment steps 14 and20). The residual glass phase includes ions of lithium and possiblysodium and potassium (if included in the composition of the precursorglass 16), and those ions are available to be exchanged with ions fromthe bath 30. This exchange of ions results in regions of compressivestress contiguous with the primary surfaces 24 a, 24 b, which arebalanced by a region of tensile stress.

In addition to imparting strength to the glass-ceramic substrate 26,lithium disilicate provides an additional pathway for the glass-ceramicsubstrate 26 to undergo ion-exchange. The lithium disilicate crystallinephase can de-crystalize, allowing the now unbound lithium ions toexchange with ions in the bath 30 of the ion-exchange. The result is arelatively high concentration of ions from the bath 30 exchanged intothe glass-ceramic article 12 near primary surfaces 24 a, 24 b of theglass-ceramic article 12. This relatively high concentration of ionsprovides high surface compression.

β-spodumene, if present as the other predominant crystalline phase,provides yet a further pathway for the glass-ceramic substrate 26 toundergo ion-exchange. β-spodumene possesses a framework structure ofcorner-connected SiO₄ and AlO₄ tetrahedra that form interlocking rings.The interlocking rings create channels that house Li ions. Those Li ionscan exchange with ions in the bath 30 of the ion-exchange, leading tosurface compression and thus strengthening.

In embodiments, the bath 30 comprises molten salt of one or more ofionic Na, K, and Ag. Example salts include nitrates of Na, K, and Ag. Inembodiments, the bath 30 includes one or more of molten NaNO₃, KNO₃, andAgNO₃. In embodiments, the bath 30 further comprises a molten salt ofionic Li (for example, LiNO₃). In embodiments, the bath 30 may be amolten salt bath including a mixture of KNO₃, NaNO₃, and LiNO₃. Inembodiments, other molten salts of ionic Na and K may be used in thebath 30, such as, for example sodium or potassium nitrites, phosphates,or sulfates. In embodiments, the bath 30 includes an additive oradditives, such as silicic acid (e.g., 1 wt % or less silicic acid).

In embodiments, the molten bath 30 includes at least 90 wt % NaNO₃. Inembodiments, the bath 30 includes 90 wt %, 91 wt %, 92 wt %, 93 wt %, 94wt %, 95 wt %, 96 wt %, 97 wt %, 98 wt %, 99 wt %, 99.9 wt %, or 100 wt% NaNO₃, or any range including any two of those values (e.g., 91 wt %to 98 wt % NaNO₃, 92 wt % to 99 wt % NaNO₃).

The molten baths described herein may include lithium, such as in theform of LiNO₃. In embodiments, the bath may include LiNO₃ in an amountfrom 0.01 wt % to 1 wt %, such as 0.1 wt % to 0.9 wt %, 0.2 wt % to 0.8wt %, 0.3 wt % to 0.7 wt %, 0.4 wt % to 0.6 wt %, 0.1 wt % to 0.5 wt %,and any ranges formed from any of these values.

In embodiments, the step 28 of the ion-exchange treatment comprises afirst ion-exchange treatment in which a first bath 30 comprises at least98 percent by weight of a salt of ionic Na (e.g., NaNO₃) and a secondion-exchange treatment in which a second bath 30 comprises a salt ofionic potassium or silver (e.g., KNO₃ or AgNO₃), or salts of both ionicpotassium and silver (e.g., KNO₃ and AgNO₃). The KNO₃ or other salts ofionic K in the second bath 30 impart a spike in compressive stress atthe primary surfaces 24 a, 24 b. In embodiments, the second bath 30comprises at least 60 wt % KNO₃. In embodiments, the second bath 30comprises 60 wt %, 65 wt %, 70 wt %, 75 wt %, 80 wt %, 85 wt %, 90 wt %,95 wt %, 98 wt %, 99 wt %, or 100 wt % KNO₃, or any range including anytwo of those values (e.g., 70 wt % to 98 wt % KNO₃, 80 wt % to 100 wt %KNO₃, etc.). In embodiments, the second bath 30 comprises a eutecticmixture of KNO₃ and NaNO₃. In embodiments, the second bath 30 comprises,exclusive of additives, 60 wt % KNO₃ and 40 wt % NaNO₃, 65 wt % KNO₃ and35 wt % NaNO₃, 70 wt % KNO₃ and 30 wt % NaNO₃, 75 wt % KNO₃ and 25 wt %NaNO₃, 80 wt % KNO₃ and 20 wt % NaNO₃, 85 wt % KNO₃ and 15 wt % NaNO₃,90 wt % KNO₃ and 10 wt % NaNO₃, 95 wt % KNO₃ and 5 wt % NaNO₃, or 99 wt% KNO₃ and 1 wt % NaNO₃, or any range including those pairs of values(e.g., 65 wt % to 80 wt % KNO₃ and 35 wt % to 20 wt % NaNO₃, 75 wt % to90 wt % KNO₃ and 25 wt % to 10 wt % NaNO₃, etc.).

The AgNO₃ or other salts of ionic Ag in the second bath 30 impart theglass-ceramic article 12 with antimicrobial properties. In embodiments,the second bath 30 is a molten mixture of AgNO₃ and KNO₃. Inembodiments, the second bath 30 comprises, exclusive of additives, amolten mixture of 5 wt % AgNO₃, 10 wt % AgNO₃, 20 wt % AgNO₃, 30 wt %AgNO₃, 40 wt % AgNO₃, or 50 wt % AgNO₃, with the balance being KNO₃, orany range including any two of those weight percentages of AgNO₃ withthe balance being KNO₃. In embodiments, the second bath 30 comprises,exclusive of additives, a molten mixture of 5 wt % AgNO₃, 10 wt % AgNO₃,20 wt % AgNO₃, 30 wt % AgNO₃, 40 wt % AgNO₃, or 50 wt % AgNO₃, with thebalance being NaNO₃ and KNO₃, or any range including any two of thoseweight percentages of AgNO₃ with the balance being NaNO₃ and KNO₃.

As a result of this two-step ion-exchange treatment, (i) a first portionof the thickness 22 of the glass-ceramic article 12 comprises a greatermole percentage of K₂O or Ag₂O than Na₂O and (ii) a second portion ofthe thickness 22 of the glass-ceramic article 12 comprises a greatermole percentage of Na₂O than K₂O or Ag₂O.

In embodiments a mixed bath may be employed in the ion-exchangetreatment of the glass-ceramic substrate. The use of a mixed bath mayproduce a stress profile with potassium enriched surface region and asodium enriched region extending deeper than the surface region, eachregion being characterized by compressive stress. In embodiments the ionexchange bath may include a mixture of NaNO₃, KNO₃, and LiNO₃. The mixedbath may include NaNO₃ in any appropriate amount, such as in the rangeof 10 wt % to 98 wt %, 20 wt % to 90 wt %, 30 wt % to 80 wt %, 40 wt %to 70 wt %, 50 wt % to 60 wt %, and any ranges formed from any of thesepairs of values. The mixed bath may include KNO₃ in any appropriateamount, such as in the range of 10 wt % to 98 wt %, 20 wt % to 90 wt %,30 wt % to 80 wt %, 40 wt % to 70 wt %, 50 wt % to 60 wt %, and anyranges formed from any of these pairs of values. The mixed bath mayinclude LiNO₃ in an amount from 0.01 wt % to 1 wt %, such as 0.1 wt % to0.9 wt %, 0.2 wt % to 0.8 wt %, 0.3 wt % to 0.7 wt %, 0.4 wt % to 0.6 wt%, 0.1 wt % to 0.5 wt %, and any ranges formed from any of these values.In embodiments, the mixed bath includes 40 wt % NaNO₃, 60 wt % KNO₃, and0.1 wt % LiNO₃.

In embodiments, the bath 30 has a temperature of 380° C. to 500° C. Inembodiments, the bath 30 has a temperature of 380° C., 390° C., 400° C.,410° C., 420° C., 430° C., 440° C., 450° C., 460° C., 470° C., 480° C.,490° C., or 500° C., or any range including any two of thosetemperatures (e.g., 410° C.-470° C., 420° C.-500° C., etc.).

In embodiments, the glass-ceramic substrate 26 contacts the bath 30 fora time period of 3 hours to 48 hours. In embodiments, the time period is3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours,11 hours, 12 hours, 13 hours, 14 hours, 15 hours, 16 hours, 17 hours, 18hours, 19 hours, 20 hours, 21 hours, 22 hours, 23 hours, 24 hours, 25hours, 26 hours, 27 hours, 28 hours, 29 hours, 30 hours, 31 hours, 32hours, 33 hours, 34 hours, 35 hours, 36 hours, 37 hours, 38 hours, 39hours, 40 hours, 41 hours, 42 hours, 43 hours, 44 hours, 45 hours, 46hours, 47 hours, or 48 hours, or any range including any two of thosetime periods (e.g. 4 hours to 27 hours, 10 hours to 25 hours, etc.).

The ion-exchange treatment can occur by dipping the glass-ceramicsubstrate 26 into the bath 30, spraying the bath 30 onto theglass-ceramic substrate 26, or otherwise physically contacting theglass-ceramic substrate 26 with the bath 30.

After the ion-exchange treatment, it should be understood that thecomposition of the glass-ceramic article 12 at the primary surfaces 24a, 24 b may be different than the composition of glass-ceramic substrate26 before the ion-exchange treatment. This results from the migration ofdifferent ions between the glass-ceramic substrate 26 and the bath 30.However, the composition of the glass-ceramic article 12 at acenter-volume 32 of the glass-ceramic article 12 will, in embodiments,be the least influenced by the ion-exchange treatment and may have acomposition substantially the same as or the same as the glass-ceramicsubstrate 26. The center-volume 32 of the glass-ceramic article 12encompasses a point 34 halfway through the thickness 22 between theprimary surfaces 24 a, 24 b, and at least 0.5 mm away from any lateraledge.

In embodiments, the ion-exchange treatment step 28 does notsignificantly alter the composition of the glass-ceramic article 12 atthe center-volume 32 of the glass-ceramic article 12. In other words,the composition of the glass-ceramic article 12 at the center-volume 32is generally the same as the composition of the glass-ceramic substrate26 before the glass-ceramic substrate 26 undergoes ion-exchangetreatment, which itself is the same as the precursor glass 16. Thecomposition of the center-volume 32 of an ion-exchanged glass-ceramicarticle 12 can be determined by microprobe by performing a line scanfrom primary surface 24 a to primary surface 24 b and determining thecomposition at the center. The crystalline phase assemblage at thecenter-volume 32 can be determined from Xray diffraction using Rietveldanalysis, unless otherwise specified. The glass-ceramic article 12 mayadopt the thickness 22 of the precursor glass 16, and in embodiments is0.3 mm to 1.0 cm, such as 0.3 mm to 2.0 mm. In embodiments, thethickness of the glass-ceramic article 12 is 0.3 mm, 0.4 mm, 0.5 mm, 0.6mm, 0.7 mm, 0.8 mm, 0.9 mm, 1.0 mm, 1.1 mm, 1.2 mm, 1.3 mm, 1.4 mm, 1.5mm, 1.6 mm, 1.7 mm, 1.8 mm, 1.9 mm, or 2.0 mm, or any range includingany two of those thicknesses (e.g., 0.5 mm to 1.2 mm, 0.6 mm to 1.0 mm,or 0.9 mm to 1.1 mm, etc.).

In embodiments, as a result of the ion-exchange treatment step 28,sodium ions are present through the entirety of the thickness 22 of theglass-ceramic article 12, even when the composition of the precursorglass 16 was substantially free of Na₂O. The mole percentage of Na₂O inthe glass-ceramic article 12 decreases from the primary surfaces 24 a,24 b towards the center-volume 32. This feature can be achieved with theglass-ceramic substrates 26 described herein by utilizing a precursorglass 16 having thickness 22 of, for example, 0.3 mm to 2.0 mm. Inaddition, this feature can be achieved through adjusting one or both ofthe temperature of the bath 30 and the time-period that theglass-ceramic substrate 26 is contacting the bath 30. In general, thehigher the temperature of the bath 30, the shorter the period of timecan be to achieve this feature. In general, the longer the period oftime that the glass-ceramic substrate 26 is in the bath 30, the lowerthe temperature of the bath 30 can be to achieve this feature.

In embodiments, as a result of the ion-exchange treatment step 28, thecomposition of a portion of the glass-ceramic article 12 from one orboth of the primary surfaces 24 a, 24 b into the thickness 22 comprisesover 10 mol % Na₂O (on an oxide basis). The mole percentage of Na₂Odecreases from the primary surfaces 24 a, 24 b toward the center-volume32. This feature can be achieved with the glass-ceramic substrates 26described herein when the bath 30 includes approximately 100 percentmolten NaNO₃ and is substantially free of lithium. The elevated molepercentage of Na₂O near the primary surfaces 24 a, 24 b can be part of aspike in Na₂O concentration resulting from the above-describedamorphization of the lithium disilicate crystalline phase near theprimary surfaces 24 a, 24 b.

In embodiments, the molten salt bath 30 of the ion-exchange treatmentcomprises greater than 98 percent by weight NaNO₃ and 0.01 to 1 percentby weight LiNO₃. In these embodiments, the bath 30 has a temperature of450° C. to 500° C., such as 450° C., 460° C., 470° C., 480° C., 490° C.,or 500° C., or any range between any two of those temperatures. In theseembodiments, the bath 30 contacts the glass-ceramic substrate 26 for atime period of 4 hours to 8 hours, such as 4 hours, 5 hours, 6 hour, 7hours, or 8 hours, or any range including any two of those time periods.In these embodiments, as a result of the ion-exchange treatment step 28,7 mole percent Na₂O is the maximum concentration of Na₂O at any depthinto the thickness 22 of the glass-ceramic article 12, and sodium ionsare present within the glass-ceramic article 12 to a depth of at least15 percent of the thickness 22 from the primary surfaces 24 a, 24 b. Inaddition, the concentration of Na₂O within the glass-ceramic article 12decreases as a function of depth into the thickness 22 of theglass-ceramic article 12 from the primary surfaces 24 a, 24 b. Inembodiments, the composition of the precursor glass 16 was substantiallyfree of Na₂O. In embodiments, the 7 mole percent Na₂O is the maximumconcentration of Na₂O at any depth into the thickness 22 of theglass-ceramic article 12, and sodium ions are present within theglass-ceramic article 12 to a depth of at least 25 percent of thethickness 22 from the primary surfaces 24 a, 24 b

In embodiments, the glass-ceramic article 12 exhibits a ring-on-ringload-to-failure of at least 120 kgf, such as 110 kgf to 130 kgf. Thering-on-ring load-to-failure test is a flexural strength measurementknown in the art for testing flat glass and glass ceramic specimens andis described in ASTM C1499-09(2013), entitled “Standard Test Method forMonotonic Equibiaxial Flexural Strength of Advanced Ceramics at AmbientTemperature,” which is incorporated herein by reference. The higher thering-on-ring load-to-failure value, the greater the glass-ceramicarticle 12 resists fracture. The greater the glass-ceramic article 12 isto resisting fracture, the greater the durability of the application towhich the glass-ceramic article 12 is applied.

In embodiments, after being abraded with SiC particles (90 grit) at anabrasion pressure of 45 psi, the glass-ceramic article 12 exhibits aring-on-ring load-to-failure of at least 80 kgf, such as 80 to 100 kgfor 80 to 90 kgf. The SiC particles are delivered to the glass sampleusing the method and apparatus described in Annex A2, entitled “AbrasionProcedures,” of ASTM C158-02(2012), entitled “Standard Test Methods forStrength of Glass by Flexure (Determination of Modulus of Rupture),”which is incorporated herein by reference. The higher the ring-on-ringload-to-failure value after abrasion, the greater the glass-ceramicarticle 12 resists fracture after being abraded. In many applications,the glass-ceramic article 12 is prone to being abraded over time. Forexample, the glass-ceramic article 12 applied to an electronic devicesuch as a smart phone can accumulate many small defects over time (suchas from keys or coins abrading the glass-ceramic article 12). The higherthe ring-on-ring load-to-failure after abrasion, the more resistance tofracture the glass-ceramic article 12 retains despite being abraded insuch a manner.

EXAMPLES

Examples 1-14. A precursor glass was formed from each of thecompositions detailed in Table 1 below designated as Examples 1-14. Theinternal liquidus temperature for the precursor glasses of Examples 1-11was measured and reported below. The internal liquidus temperaturegenerally increases as ZrO₂ content in the composition of the precursorglass increases.

The liquidus viscosity was measured and reported below for the precursorglasses of Examples 1-4. The liquidus viscosity generally decreases asZrO₂ content in the composition of the precursor glass increases.

The liquidus phase was determined and reported below for the precursorglasses of Examples 1-9. Lithiophosphate and β-spodumene materialized asthe liquidus phases for the precursor glass of Example 1, which included2.0 mol % ZrO₂ in the composition. However, when the compositionincluded 3.0 mol % or more ZrO₂, as for the precursor glasses ofExamples 2-9, zircon materialized as the liquidus phase.

Pursuant to the method above, the precursor glasses of Examples 1-14were maintained in an environment having a first temperature of 700° C.for a first time period of 2 hours (for Examples 1-11) or 4 hours (forExamples 12-14). Then, the precursor glasses were maintained in theenvironment having a second temperature for a second time period, as setforth below as the “Ceramming Cycle.” More specifically, the precursorglasses of Examples 1 and 2 were maintained in the environment havingthe second temperature of 875° C. for the second time period of 4 hours.The precursor glasses of Examples 3-11 were maintained in theenvironment having the second temperature of 900° C. for the second timeperiod of 4 hours. The precursor glasses of Examples 12-14 weremaintained in the environment having the second temperature of 875° C.for the second time period of 1 hour. The precursor glasses thus becameglass-ceramic substrates.

The phase assemblages for the glass-ceramic substrates of Examples 1-14were determined and are set forth in Table 1 below. X-ray diffractionwas utilized to determine the phase assemblage using Rietveld analysis.X-ray diffraction analysis techniques are known to those in the art,using such commercially available equipment as the model PW1830 (Cu Kαradiation) diffractometer manufactured by Philips, Netherlands. Lithiumdisilicate (“LS2” in Table 1 below) was one of the two predominantcrystalline phases for the glass-ceramic substrates of all of Examples1-14. β-spodumene was the other of the two predominant crystallinephases for the glass-ceramic substrates of Examples 1-6 (in which theprecursor glass composition was substantially free of TiO₂ and included3.4 mol % to 4.3 mol % Al₂O₃) and Examples 12-14 (in which the precursorglass composition included 4.9 mol % Al₂O₃ and 2.0 mol % TiO₂). β-quartzwas the other of the two predominant crystalline phases (instead ofβ-spodumene) for the glass-ceramic substrates of Examples 7-11, wherethe precursor glass composition included 1.0 to 2.9 mol % Al₂O₃. Theglass-ceramic substrates of all of Examples 1-14 included tetragonalZrO₂ (“t-ZrO₂”) and lithiophosphate (“L3P”) as crystalline phases.Monoclinic ZrO₂ (“m-ZrO₂”) was present as a crystalline phase of theglass-ceramic substrates of Examples 1-11. Rutile was present as acrystalline phase of the glass-ceramic substrates of Example 12, wherethe mole percentage of TiO₂ exceeded the mole percentage of ZrO₂ in thecomposition of the precursor glass.

The general color appearance was recorded as “white” for theglass-ceramic substrates of all of Examples 1-14. In all of Examples1-14, the composition of the precursor glass included 1.8 mol % to 5.0mol % ZrO₂.

The fracture toughnesses (“K_(1c)”) of the glass-ceramic substrates ofExamples 1 and 2 were measured and recorded. The glass-ceramic substrateof Example 1, made from a precursor glass composition comprising 2.0 mol% ZrO₂, had a fracture toughness of 1.6 MPa·m^(1/2). The glass-ceramicsubstrate of Example 2, made from a precursor glass compositioncomprising 3.0 mol % ZrO₂, had a fracture toughness of 2.2 MPa·m^(1/2).

The Poisson's ratio, shear modulus, and Young's modulus for theglass-ceramic substrates of Examples 1, 2, and 4 were determined andrecorded as set forth in Table 1. These properties were determinedpursuant to the methods described in ASTM C1259 “Standard Test Methodfor Dynamic Young's Modulus, Shear Modulus, and Poisson's Ratio forAdvanced Ceramics by Impulse Excitation of Vibration,” ASTMInternational, Conshohocken, Pa., US, which is incorporated herein byreference.

The Vickers hardness test value (“HV”) for the glass-ceramic substrateof Example 1 was determined and recorded as set forth below in Table 1.This property was determined pursuant to the methods described in ASTMC1327 (and its progeny, all herein incorporated by reference) entitled“Standard Test Methods for Vickers Indentation Hardness of AdvancedCeramics,” ASTM International, Conshohocken, Pa., US. The contents ofASTM C1327, ASTM C1259, ASTM E1304-97, ASTM C1499-09(2013), and ASTMC158-02(2012), Annex 2, are incorporated herein by reference in theirentirety.

TABLE 1 Example Oxide (mol %) 1 2 3 4 5 6 7 SiO₂ 70.7 70.0 69.7 69.368.6 68.9 69.3 Al₂0₃ 4.3 4.3 4.2 4.2 4.2 3.4 2.9 Li₂O 22.1 21.9 21.821.7 21.5 21.5 21.6 Na₂O 0.0 0.0 0.0 0.0 0.0 0.0 0.0 P₂O₅ 0.9 0.9 0.90.9 0.9 1.2 1.2 ZrO₂ 2.0 3.0 3.4 3.9 4.9 4.9 4.9 TiO₂ 0.0 0.0 0.0 0.00.0 0.0 0.0 SilO₂ 0.0 0.0 0.0 0.0 0.0 0.1 0.1 Internal liquidus 10301100 1160 1200 1275 1290 1255 (° C.) Liquidus 5400 2850 1140 880 —viscosity (poise) Liquidus phase L3P/spd zircon Zircon Zircon ZirconZircon Zircon Ceramming 700° C.-2 h 700° C.-2 h 700° C.-2 h 700° C.-2 h700° C.-2 h 700° C.-2 h 700° C.-2 h cycle 875° C.-4 h 875° C.-4 h 900°C.-4 h 900° C.-4 h 900° C.-4 h 900° C.-4 h 900° C.-4 h Phaseβ-spodumene, β-spodumene, β-spodumene, β-spodumene, β-spodumene,β-spodumene, β-quartz, assemblage LS2, t-ZrO₂, LS2, t-ZrO₂, LS2, t-ZrO₂,LS2, t-ZrO₂, LS2, t-ZrO₂; LS2, t-ZrO₂, LS2, t-ZrO₂, m-ZrO₂, L3P m-ZrO₂,L3P m-ZrO₂, L3P m-ZrO₂, L3P m-ZrO₂, L3P β-quartz, m-ZrO₂, L3P; m-ZrO₂,L3P Appearance White White White White White White White K_(1c) (MPa ·m^(1/2)) 1.6 2.2 Poisson's ratio 0.24 0.24 0.24 Shear modulus 38.7 39.039.2 (GPa) Young's 95.6 96.7 97.4 modulus (GPa) HV (kgf/mm²) 750 ExampleOxides (mol %) 8 9 10 11 12 13 14 SiO₂ 69.6 69.9 70.9 70.6 70.6 70.370.0 Al₂O₃ 2.5 2.0 1.0 1.5 4.9 4.9 4.9 Li₂O 21.8 21.9 22.2 22.1 19.419.3 19.2 Na₂O 0.0 0.0 0.0 0.0 0.2 0.2 0.2 P₂O₅ 1.2 1.2 0.9 0.9 1.0 1.01.0 ZrO₂ 4.9 4.9 5.0 5.0 1.8 2.2 2.6 TiO₂ 0.0 0.0 0.0 0.0 2.0 2.0 2.0SnO₂ 0.1 0.1 0.0 0.0 0.1 0.1 0.1 Internal 1245 1225 1180 1185 Liquidus(° C.) Liquidus phase Zircon Zircon Ceramming 700° C.-2 h 700° C.-2 h700° C.-2 h 700° C.-2 h 700° C.-4 h 700° C.-4 h 700° C.-4 h cycle 900°C.-4 h 900° C.-4 h 900° C.-4 h 900° C.-4 h 875° C.-1 h 875° C.-1 h 875°C.-1 h Phase β-quartz, β-quartz, β-quartz, β-quartz, β-spodumene,β-spodumene, β-spodumene, assemblage LS2, t- LS2, t- LS2, t- LS2, t-LS2, t-ZrO₂, LS2, t-ZrO₂, LS2, t-ZrO₂, ZrO₂, m- ZrO₂, m- ZrO₂, m- ZrO₂,m- β-quartz, L3P, β-quartz, L3P β-quartz, L3P ZrO₂, L3P ZrO₂, L3P ZrO₂,L3P ZrO₂, L3P rutile Appearance White White White White White WhiteWhite

Examples 1 (continued) and 1A-1D. Samples of the precursor glass ofExample 1 were, pursuant the method above, again subjected to cerammingcycles, this time including variations in first temperature, first timeperiod, and second temperature (a second time period of 4 hours wasmaintained as a constant). The ceramming cycles implemented pursuant tothe method are set forth in Table 2 below. The samples are designated asExamples 1 and 1A-1D.

CIELAB color space coordinates (“Color coordinates”) (e.g., L*, a*, andb*) for describing the color exhibited by the glass-ceramic substratesof Examples 1 and 1A-1D were determined using 0.8 mm in thicknesssamples with the Color i7 Spectrophotometer using an F02 illuminantunder SCI UVC condition. The CIELAB color space coordinates for Examples1 and 1A-1D are set forth in Table 2 below.

The average opacity (“Opacity %”) throughout the wavelength range of 400nm to 700 nm of the glass-ceramic substrates of Examples 1 and 1A-1Dwere determined using the contrast method with the Color i7Spectrophotometer. The average opacity for Examples 1 and 1A-1D are setforth in Table 2 below. The glass-ceramic substrate of Example 1D,cerammed using the highest first temperature of 750° C. at a first timeperiod of 4 hours, resulted in the greatest opacity (95%) of this set ofexamples with 2.0 mol % ZrO₂ and no TiO₂, while still havingsubstantially white CIELAB color coordinates. The glass-ceramicsubstrates of Examples 1A and 1B exhibited CIELAB color coordinatesclosest to pure white, while being substantially opaque at 80 percentand 85 percent average opacity, respectively.

TABLE 2 Example 1A 1B 1 1C 1D Cer- 600° C.- 625° C.- 700° C.- 650° C.-750° C.- amming 2 h 2 h 2 h 4 h 4 h cycle 875° C.- 875° C.- 875° C.-865° C.- 865° C.- 4 h 4 h 4 h 4 h 4 h Color L* = 96.0 L* = 96.0 L* =96.5 L* = 93.7 L* = 95.3 co- a* = −0.3 a* = −0.3 a* = −0.4 a* = −0.8 a*= −0.5 ordinates b* = 0.3 b* = 0.3 b* = 2.6 b* = −0.1 b* = −0.5 Opacity80 85 90 78.5 95 (%)

Example 1E. Pursuant to the method of this disclosure, another sample ofthe precursor glass of Example 1 having a thickness of 0.8 mm from Table1 above was cerammed using a first temperature of 760° C. for a firsttime period of 4 hours, and a second time period of 875° C. for a secondtime period of 4 hours. This sample is designated as Example 1E. Theenvironment in which the precursor glass was maintained was heated tothe first temperature of 760° C. at a rate of 5° C. per minute.

The phase assemblage of the resulting glass-ceramic substrate wasdetermined via X-ray diffraction using Rietveld analysis. The plot ofthe reflected intensities (“Intensity”) as a function of the detectorangle (“2 theta (°)”) is reproduced as FIG. 4. The plot revealsβ-spodumene and lithium disilicate as the two predominant crystallinephases (by weight percentage) of the glass-ceramic substrate. The plotadditionally reveals tetragonal ZrO₂ (“t-ZrO₂”) and lithiophosphate ascrystalline phases.

A scanning electron microscope was utilized to image the glass-ceramicsubstrate of Example 1E. Several images are reproduced herein as FIGS.5A and 5B. In the images, the white spots correspond to the tetragonalZrO₂ crystalline phase, the needles correspond to the lithium disilicatecrystalline phase, and the grey blocks correspond to the β-spodumenecrystalline phase.

Pursuant to the method above, three samples of the glass-ceramicsubstrate of Example 1E were subjected to an ion-exchange treatment in abath of 100 percent NaNO₃ at a temperature of 470° C., each with adifferent period of time in the bath. A first sample was in the bath for4 hours. A second sample was in the bath for 7 hours. A third sample wasin the bath for 16 hours. The ion-exchange treatment transformed theglass-ceramic substrates into glass-ceramic articles, each with adifferent profile of concentration of sodium ions as a function of depthinto the glass-ceramic article (and thus each with a differentcompressive stress profile).

An electron microprobe was utilized to characterize composition(particularly Na₂O, demonstrative of sodium ions) of the glass-ceramicarticles of Example 1E as a function of depth into the thickness of theglass-ceramic articles. A graph of the results is reproduced as FIG. 6.For the sample that was in the bath for 16 hours, sodium ions extendthrough the entire thickness of the glass-ceramic article, although theprecursor glass was substantially free of Na₂O. For each of the samples,the composition of portions of the glass-ceramic article from theprimary surfaces into the thickness comprises over 10 percent Na₂O.These portions are from the primary surfaces into approximately 10 μminto the thickness. Near the primary surfaces, the rate of change ofmole percentage of Na₂O as a function of position (depth) (i.e., theslope of the mole percentage of Na₂O) within the thickness is higherthan the rate of change (i.e., the slope) further within the thicknessof the glass-ceramic article. The higher rate of change (i.e., steeperslope) is illustrated as spikes in concentration in FIG. 6.

A fourth sample of the glass-ceramic substrate of Example 1E wassubjected to an ion-exchange treatment in a bath of 100 percent NaNO₃ ata temperature of 470° C. for a time period of 6 hours. The ring-on-ringload-to-failure was measured. The plot reproduced at FIG. 7 is a Weibulldistribution, which represents the probability of glass failure(fracture) due to a given stress. As illustrated, the glass-ceramicsubstrate (having not undergone the ion-exchange step of the method) islikely to fail in response to loads that are about 50 percent less thanthe loads likely to cause the glass-ceramic article (having undergonethe ion-exchange step of the method) to fail. For the glass-ceramicarticle of the fourth sample of Example 1E, the load-to-failure is atleast 120 kgf.

A series of fifth samples of the glass-ceramic substrate of Example 1Ewere again (like the fourth sample) subjected to an ion-exchangetreatment step in a bath of 100 percent NaNO₃ at a temperature of 470°C. for a time period of 6 hours. The resulting glass-ceramic articleswere then abraded with SiC particles, each sample being abraded with SiCparticles projected at a different air pressure. The abraded sampleswere then subjected to a ring-on-ring load-to-failure test. The resultsare graphically reproduced at FIG. 8. The results illustrate that theload-to-failure without abrasion (0 psi) was over 130 kgf, and theload-to-failure with abrasion at 45 psi was over 80 kgf.

The graph of FIG. 8 additionally includes results for a ComparativeExample. The precursor glass of the Comparative Example had a thicknessof 0.8 mm and a composition that included 69.2 mol % SiO₂, 12.6 mol %Al₂O₃, 1.8 mol % B₂O₃, 7.7 mol % Li₂O, 0.4 mol % Na₂O, 2.9 mol % MgO,1.7 ZnO, 3.5 TiO₂, and 0.1 SnO₂. The precursor glass was cerammed at afirst temperature of 780° C. for a first time period of 2 hours, andthen a second temperature of 975° C. for a second time period of 4hours, resulting in a glass-ceramic substrate. The glass-ceramicsubstrate had a predominate crystalline phase of β-spodumene, and rutileand gahnite as minor crystalline phases. The glass-ceramic substrate wasthen ion-exchanged in a pure NaNO₃ bath 30 at 390° C. for 3.5 hours,resulting in a glass-ceramic article. The glass-ceramic article was thensubjected to the same load-to-failure test, including after abrasionwith SiC particles at various air pressures. The results illustratethat, although the Comparative Example had a higher load-to-failurewithout abrasion (over 150 kgf), the Comparative Example retained lessstrength at all abrasion pressures tested. For example, after abrasionat a pressure of 45 psi, the glass-ceramic article of the ComparativeExample failed at about 30 kgf, whereas the glass-ceramic article ofExample 1E failed at over 80 kgf. Without being bound by theory, it isbelieved that the presence of lithium disilicate as a predominatecrystalline phase and the presence of tetragonal ZrO₂ as an additionalcrystalline phase in the glass-ceramic article of Example 1E providedExample 1E with greater retained strength.

Example 1 (continued). Pursuant to the method above, two samples of theglass-ceramic substrate of Example 1 were subjected to an ion-exchangetreatment in a bath at a temperature of 470° C. for a period of time of6 hours. For the first sample, the bath was 100 percent NaNO₃. For thesecond sample, the bath was 99.9 percent by weight NaNO₃ and 0.1 percentby weight LiNO₃.

An electron microprobe was utilized to characterize composition(particularly Na₂O, demonstrative of sodium ions) of the resultingglass-ceramic articles as a function of depth into the thickness of theglass-ceramic articles. A graph of the results is reproduced as FIG. 9.As mentioned above, it is believed that the lithium disilicatecrystalline phase near the primary surfaces becomes amorphous, whichfrees lithium ions to migrate from the glass-ceramic substrate to thebath and thus provides space for sodium ions to migrate from the bath tothe glass-ceramic substrate. The result is the relatively large rate ofchange of mole percentage of Na₂O (i.e., the spike in slope) near theprimary surfaces (e.g., from the primary surfaces to 25 μm into thethickness), for the sample ion-exchanged in the bath with pure NaNO₃.

As the graph of FIG. 9 illustrates for the second sample, including anamount of LiNO₃ in the bath suppresses generation of the amorphous layerfrom the lithium disilicate crystallization phase. Accordingly, no spike(i.e., relatively high rate of change in concentration) in the molepercentage of Na₂O near the primary surfaces results. Sodium ions stillmigrate from the bath into the thickness of the glass-ceramic substrate,resulting here in the presence of sodium ions within the glass-ceramicarticle to a depth of at least 15 percent (and even 25 percent) of thethickness from the primary surfaces (e.g., at least 120 μm of the 800 μmthickness, or at least 200 μm of the 800 μm thickness). However, thereis no relatively large rate of change (i.e., no spike) of concentrationof Na₂O near the primary surfaces and the concentration of Na₂O has amaximum of less than 7 mol % (i.e., about 6 mol %), which occurs at ornear the primary surfaces.

Additional Examples. Additional glass-ceramic substrates and articleswere produced from two similar precursor glass compositions. Theanalyzed precursor glass compositions are provided in Table 3 below inmol %. It should be noted that Na₂O and K₂O were not purposely added tothe glass composition but it is understood that low levels of Na₂O andK₂O may be introduced as contaminants in batch materials.

TABLE 3 Composition X Y SiO₂ 70.8 69.9 Al₂O₃ 4.2 4.2 P₂O₅ 0.9 0.8 Li₂O21.8 22.7 Na₂O 0.1 0.1 K₂O 0.1 0.1 ZrO₂ 1.9 2.0 SnO₂ 0.2 0.2

In addition to the compositional differences reported in Table 3, theglass compositions included differing concentrations of beta-OH, withComposition X having a lower beta-OH concentration than Composition Y.This difference in beta-OH concentration may result in different phaseassemblages when cerammed to form glass-ceramic substrates. Thedifference in beta-OH concentration may be a result of a differentconcentration of beta-OH in the raw materials utilized to form the meltsor due to a difference in melting conditions.

Glass-ceramic substrates were formed by ceramming precursor glassesformed from the compositions of Table 3, and the resulting phaseassemblage was determined as described herein, as well as the colorcoordinates and opacity. The phase assemblage is reported in terms of wt%, and the produced glass-ceramic substrates include a low level of aresidual glass phase even when not quantifiable by Rietveld analysis.Additionally, the total amount of crystalline ZrO₂ is reported for thesamples. The analysis indicated the presence of tetragonal ZrO₂. Theceramming treatment and the measurement results are reported in Table 4.All substrates had a thickness of 0.8 mm.

TABLE 4 Sample 20 21 22 23 24 25 Composition Y Y Y Y Y Y Ceramming 700°C.-4 hrs 740° C.-4 hrs 750° C.-4 hrs 760° C.-4 hrs 780° C.-4 hrs 800°C.-4 hrs Treatment 875° C.-4 hrs 875° C.-4 hrs 875° C.-4 hrs 875° C.-4hrs 875° C.-4 hrs 875° C.-4 hrs Glass Li₂Si₂O₅ 42 43 43 43 43 43β-Spodumene 51 51 50 50 50 50 Li₂PO₄ 4.1 3.5 3.6 3.6 3.5 3.7 β-Quartztrace 0.3 0.2 0.3 trace Total ZrO₂ 2.5 3.1 3.4 3.3 3.4 3.6 L* 94.7295.87 94.42 95.89 94.84 a* −0.79 −0.59 −0.66 −0.60 −0.65 b* −0.63 0.07−0.32 −0.06 −0.47 Opacity 87 96 87 96 93 Sample 26 27 28 29 30 31Composition X X X X X X Ceramming 700° C.-4 hrs 740° C.-4 hrs 750° C.-4hrs 760° C.-4 hrs 780° C.-4 hrs 800° C.-4 hrs Treatment 875° C.-4 hrs875° C.-4 hrs 875° C.-4 hrs 875° C.-4 hrs 875° C.-4 hrs 875° C.-4 hrsGlass 11 10 3.8 Li₂Si₂O₅ 37 39 42 43 43 43 β-Spodumene 48 48 49 50 50 50Li₂PO₄ 3.4 3.6 3.8 3.8 3.7 3.6 β-Quartz 0.2 Total ZrO₂ 1.4 3.0 3.0 3.2L* 94.04 94.29 95.17 95.37 95.77 95.78 a* −0.82 −0.77 −0.62 −0.58 −0.61−0.63 b* −0.44 −0.59 −0.87 −1.02 −0.81 −0.93 Opacity 66 67 88 87 92 92

Additional samples Glass-ceramic substrates were formed by cerammingprecursor glasses formed from Composition X of Table 3, and theresulting phase assemblage was determined, as well as the colorcoordinates and opacity. The phase assemblage is reported in terms of wt%, and the produced glass-ceramic substrates include a low level of aresidual glass phase even when not quantifiable by Rietveld analysis.Additionally, the total amount of crystalline ZrO₂ is reported for thesamples. The analysis indicated the presence of tetragonal ZrO₂. ThePoisson's ratio, shear modulus, Young's modulus, and K_(1C) fracturetoughness of the glass-ceramic substrates were also measured. Theceramming treatment and the measurement results are reported in Table 5.All substrates had a thickness of 0.8 mm.

TABLE 5 Sample 32 33 34 35 36 37 Composition X X X X X X Ceramming 800°C.-4 hrs 700° C.-4 hrs 760° C.-4 hrs 700° C.-4 hrs 760° C.-4 hrs 700°C.-4 hrs Treatment 875° C.-4 hrs 850° C.-4 hrs 850° C.-4 hrs 875° C.-4hrs 875° C.-4 hrs 890° C.-4 hrs Glass 10.5 11.5 Li₂Si₂O₅ 42.0 42.0 42.636.4 42.9 36.0 β-Spodumene 51.0 51.6 48.0 49.2 49.9 48.5 Li₂PO₄ 3.7 4.03.8 3.4 4.0 3.4 β-Quartz 0.2 1.0 Virgilite 1.0 Total ZrO₂ 3.1 2.4 3.70.4 3.2 0.6 Poisson's Ratio 0.238 0.233 0.232 0.232 0.238 0.239 ShearModulus 5.64 5.63 5.70 5.58 5.62 5.59 (Mpsi) Young's Modulus 13.97 13.8814.03 13.75 13.91 13.85 (Mpsi) K_(IC) 1.541 1.415 1.409 1.447 1.5351.564 (MPa · m^(1/2)) Sample 38 39 40 41 Composition X X X X Ceramming760° C.-4 hrs 760° C.-4 hrs 800° C.-4 hrs 800° C.-4 hrs Treatment 890°C.-4 hrs 825° C.-4 hrs 890° C.-4 hrs 950° C.-4 hrs Glass Li₂Si₂O₅ 41.9β-Spodumene 51.3 Li₂PO₄ 4.0 β-Quartz Virgilite Total ZrO₂ 2.7 Poisson'sRatio 0.237 Shear Modulus 5.63 (Mpsi) Young's Modulus 13.93 (Mpsi)K_(IC) 1.655 1.308 1.720 1.812 (MPa · m^(1/2))

Glass-ceramic substrate Sample 32 was processed by etching to reveal thecrystalline phases to prepare for SEM analysis. The resulting SEM imagesare provided in FIGS. 10 and 11, with FIG. 11 being at a highermagnification.

To demonstrate the chemical strengthening ability of the glass-ceramicsubstrates, glass-ceramic substrates according to Sample 32 with variousthicknesses were ion exchanged to form glass-ceramic articles thatinclude a stress profile, as reported in Table 6 below. The ion exchangewas performed by submerging the glass-ceramic substrates in a moltensalt bath, with the submersion time and bath temperatures reported inTable 6. The molten salt bath included 40% NaNO₃, 60% KNO₃, and 0.1%LiNO₃, by weight. Comparative glass-ceramic article substrate exampleswere also ion exchanged. The comparative examples were produced from aglass having Composition X and were cerammed under conditions thatproduced a glass-ceramic article with a transparent appearance.

TABLE 6 Sample 32A 32B 32C Comp. Ex. 1 Comp. Ex. 2 Comp. Ex. 3Thickness(mm) 0.8 0.8 0.4 0.8 0.4 0.4 Ion Exchange Temperature (° C.)500 470 470 500 500 500 Treatment Time(hrs) 8 9 3.5 8 4 4.5

The ion exchanged samples were then placed in a sample holder simulatinga cover glass in a mobile electronic device and dropped fromincrementally higher heights such that the sample contacts a sandpapercovered surface. The maximum drop height prior to sample failure wasrecorded for a number of samples and a mean maximum drop height wascalculated. The results of the drop test where 80 grit sandpaper wasemployed are reported in FIGS. 12 and 13, and the results of the droptest where 30 grit sandpaper was employed are reported in FIG. 14.

Variations and modifications may be made to the above-describedembodiments of the disclosure without departing substantially from thespirit and various principles of the disclosure. All such modificationsand variations are intended to be included herein within the scope ofthis disclosure and protected by the following claims.

What is claimed is:
 1. A method of manufacturing a glass-ceramic article comprising: (a) maintaining a precursor glass in an environment for a first time period of 1.75 to 4.25 hours while the environment has a first temperature of 590° C. to 820° C., the precursor glass having a composition comprising, on an oxide basis: 55-75 mol % SiO₂; 0.2-10 mol % Al₂O₃; 0-5 mol % B₂O₃; 15-30 mol % Li₂O; 0-2 mol % Na₂O; 0-2 mol % K₂O; 0-5 mol % MgO; 0-2 mol % ZnO; 0.2-3.0 mol % P₂O₅; 0.1-10 mol % ZrO₂; 0-4 mol % TiO₂; and 0-1.0 mol % SnO₂; (b) maintaining the precursor glass in the environment for a second time period of 0.75 hour to 4.25 hours while the environment has a second temperature of 850° C. to 925° C., forming a glass-ceramic substrate, wherein (i) lithium disilicate and (ii) either β-spodumene or β-quartz are the two predominant crystalline phases by weight percentage of the glass-ceramic substrate, and wherein tetragonal ZrO₂ is a crystalline phase of the glass-ceramic substrate; and (c) subjecting the glass-ceramic substrate to an ion-exchange treatment in a molten salt bath that comprises a salt of one or more of ionic Na, K, and Ag, forming a glass-ceramic article; wherein at least one of the following conditions is true: (i) the composition of the precursor glass was characterized by Na₂O+K₂O≤0.5 mol %, but sodium ions are present throughout an entire thickness of the glass-ceramic article; (ii) the composition of a portion of the glass-ceramic article from a primary surface into the thickness comprises over 10 mol % Na₂O, on an oxide basis; (iii) the bath of the ion-exchange treatment comprises greater than 98 percent by weight NaNO₃ and 0.01 to 1 percent by weight LiNO₃; and the mole percentage of Na₂O within the glass-ceramic article decreases as a function of depth into the thickness of the glass-ceramic article from the primary surface, with the maximum mole percentage of Na₂O at any depth being 7 mol % Na₂O, and sodium ions are present within the glass-ceramic article to a depth of at least 15 percent of the thickness from the primary surface; and (iv) the ion-exchange treatment comprises a first ion-exchange treatment in which a first bath comprises at least 98 percent by weight NaNO₃ and a second ion-exchange step in which a second bath comprises ions of potassium or silver; and (i) a first portion of the thickness of the glass-ceramic article comprises a mole percentage of either K₂O or Ag₂O that is greater than the mole percentage of Na₂O and (ii) a second portion of the thickness of the glass-ceramic article comprises a mole percentage of Na₂O that is greater than the mole percentage of either K₂O or Ag₂O.
 2. The method of claim 1, wherein: the precursor glass was characterized by Na₂O+K₂O≤0.5 mol %, but sodium ions are present throughout the entire thickness of the glass-ceramic article.
 3. The method of claim 1, wherein: the composition of a portion of the glass-ceramic article from the primary surface into the thickness comprises over 10 mol % Na₂O, on an oxide basis.
 4. The method of claim 1, wherein: the bath of the ion-exchange treatment comprises greater than 98 percent by weight NaNO₃ and 0.01 to 1 percent by weight LiNO₃; and the mole percentage of Na₂O within the glass-ceramic article decreases as a function of depth into the thickness of the glass-ceramic article from the primary surface, with the maximum mole percentage of Na₂O at any depth being 7 mol % Na₂O, and sodium ions are present within the glass-ceramic article to a depth of at least 15 percent of the thickness from the primary surface.
 5. The method of claim 1, wherein: the ion-exchange treatment comprises the first ion-exchange treatment in which the first bath comprises at least 98 percent by weight NaNO₃ and the second ion-exchange step in which the second bath comprises ions of potassium or silver; and (i) the first portion of the thickness of the glass-ceramic article comprises a mole percentage of either K₂O or Ag₂O that is greater than the mole percentage of Na₂O and (ii) the second portion of the thickness of the glass-ceramic article comprises a mole percentage of Na₂O that is greater than the mole percentage of either K₂O or Ag₂O.
 6. The method of claim 1, wherein: the glass-ceramic substrate exhibits a color, under an F02 illuminant, presented in CIELAB color space coordinates: L*=88 to 98; a*=−1.0 to 1; and b*=−4.0 to 4.0.
 7. A glass-ceramic substrate comprising: a composition comprising, on an oxide basis: 68.6-71.5 mol % SiO₂; 1.0-4.5 mol % Al₂O₃; 21.5-22.2 mol % Li₂O; 0.7-1.2 mol % P₂O₅; 1.5-5.0 mol % ZrO₂; and 0-1.0 mol % SnO₂; wherein (i) lithium disilicate and (ii) either β-spodumene or β-quartz are the two predominant crystalline phases by weight percentage of the glass-ceramic substrate; and wherein tetragonal ZrO₂ is a crystalline phase of the glass-ceramic substrate.
 8. The glass-ceramic substrate of claim 7, comprising: 68.6-70.9 mol % SiO₂; 1.0-4.3 mol % Al₂O₃; 0.9-1.2 mol % P₂O₅; and 3.0-5.0 mol % ZrO₂.
 9. A glass-ceramic article comprising: a composition at a center-volume comprising, on an oxide basis: 55-75 mol % SiO₂; 0.2-10 mol % Al₂O₃; 0-5 mol % B₂O₃; 15-30 mol % Li₂O; 0-2 mol % Na₂O; 0-2 mol % K₂O; 0-5 mol % MgO; 0-2 mol % ZnO; 0.2-3.0 mol % P₂O₅; 0.1-10 mol % ZrO₂; 0-4 mol % TiO₂; and 0-1.0 mol % SnO₂; wherein (i) lithium disilicate and (ii) either β-spodumene or β-quartz are the two predominant crystalline phases (by weight) of the glass-ceramic article; wherein the glass-article further comprises tetragonal ZrO₂ as a crystalline phase; and wherein at least one of the following conditions are true: (i) the composition of the glass-ceramic article from a primary surface into a thickness of the glass-ceramic article comprises over 10 mol % Na₂O, on an oxide basis, with the mole percentage of Na₂O decreasing from the primary surface towards the center-volume; and (ii) the mole percentage of Na₂O within the glass-ceramic article decreases as a function of depth into the thickness of the glass-ceramic article from the primary surface, with the maximum mole percentage of Na₂O at any depth being 7 mol % Na₂O, and sodium ions are present within the glass-ceramic article to a depth of at least 15 percent of the thickness from the primary surface.
 10. The glass-ceramic article of claim 9, wherein: the composition of the glass-ceramic article from the primary surface into the thickness of the glass-ceramic article comprises over 10 mol % Na₂O, with the mole percentage of Na₂O decreasing from the primary surface towards the center-volume.
 11. The glass-ceramic article of claim 9, wherein: the mole percentage of Na₂O within the glass-ceramic article decreases as a function of depth into the thickness of the glass-ceramic article from the primary surface, with the maximum mole percentage of Na₂O at any depth being 7 mol % Na₂O and, and sodium ions are present within the glass-ceramic article to a depth of at least 15 percent of the thickness from the primary surface.
 12. The glass-ceramic article of claim 9, wherein: the glass-ceramic article exhibits a ring-on-ring load-to-failure of at least 120 kgf.
 13. The glass-ceramic article of claim 9, wherein: after being abraded with SiC particles at an abrasion pressure of 45 psi, the glass-ceramic article exhibits a ring-on-ring load-to-failure of at least 80 kgf.
 14. The glass-ceramic article of claim 9, wherein: the composition of the glass-ceramic article at the center-volume comprises, on an oxide basis: 68.6-71.5 mol % SiO₂; 1.0-4.5 mol % Al₂O₃; 21.5-22.2 mol % Li₂O; 0.7-1.2 mol % P₂O₅; 1.5-5.0 mol % ZrO₂; and 0-0.1 mol % SnO₂, wherein the glass-ceramic article is substantially free of B₂O₃; MgO; ZnO; and TiO₂.
 15. The glass-ceramic article of claim 9, wherein: the composition of the glass-ceramic article at the center-volume comprises, on an oxide basis: 68.6-70.9 mol % SiO₂; 1.0-4.3 mol % Al₂O₃; 21.5-22.2 mol % Li₂O; 0.9-1.2 mol % P₂O₅; 2.0-5.0 mol % ZrO₂; and 0-0.1 mol % SnO₂, wherein the glass-ceramic article is substantially free of B₂O₃; MgO; ZnO; and TiO₂.
 16. The glass-ceramic article of claim 9, wherein: the composition of the glass-ceramic article at the center-volume comprises (on an oxide basis): 68.6-70.9 mol % SiO₂; 1.0-4.3 mol % Al₂O₃; 21.5-22.2 mol % Li₂O; 0.9-1.2 mol % P₂O₅; 3.0-5.0 mol % ZrO₂; and 0-1.0 mol % SnO₂.
 17. The glass-ceramic article of claim 9, wherein: the glass-ceramic article exhibits a color, under an F02 illuminant, presented in CIELAB color space coordinates: L*: 93 to 97; a*: −1.0 to 0; and b*: −1.0 to 3.0.
 18. The glass-ceramic article of claim 9, wherein: the glass-ceramic substrate has an average opacity of 79 to 96 percent throughout the wavelength range of 400 nm to 700 nm for a thickness of 0.8 mm.
 19. The glass-ceramic article of claim 9, wherein: the composition of the glass-ceramic article at the center-volume comprises, on an oxide basis, 3.4 to 4.3 mol % Al₂O₃; and lithium disilicate and β-spodumene are the two predominant by weight crystalline phases of the glass-ceramic article.
 20. The glass-ceramic article of claim 9, wherein: the composition of the glass-ceramic article at the center-volume comprises, on an oxide basis: 70.0-70.6 mol % SiO₂; 4.85-4.95 mol % Al₂O₃; 19.2-19.4 mol % Li₂O; 0.195-0.205 mol % Na₂O; 0.9-1.1 mol % P₂O₅; 1.8-2.6 mol % ZrO₂; 1.9-2.1 mol % TiO₂; and 0.09-0.11 mol % SnO₂, wherein the glass-ceramic article at the center-volume is substantially free of B₂O₃; K₂O; MgO; and ZnO; and lithium disilicate and β-spodumene are the two predominant crystalline phases by weight of the glass-ceramic article. 